How to resize Apple partition?
Disk Utility for macOS Sierra: Partition a physical disk using Disk Utility

Please make sure to preform a backup prior to partitioning. Although a standard process, there's always an increased risk of corruption or failure when modifying partitions. But this shouldn't be an issue as you have been backing up regularly........right?


  Disk Utility for macOS Sierra: Partition a physical disk using Disk
  
  Utility
  
  Partitioning a storage device divides it into individual partitions,
  which are listed as separate volumes under the Devices section in the
  Finder sidebar. You may need to partition a disk if you want to
  install multiple operating systems or if you need to change the
  device’s format.
  
  If you’re partitioning your internal physical disk because you want to
  install Windows, use Boot Camp Assistant.
  
  WARNING: To prevent the loss of data on your Fusion Drive, don’t
  connect it to a Mac that’s using a version of OS X earlier than
  v10.8.5. For more information, see the Apple Support article Only
  connect OS X Mavericks Fusion drives to OS X Mountain Lion v10.8.5 or
  later.
  
  
  
  You can easily create new partitions on a device with at least one
  volume that contains data, if it has space available.
  
  Important: As a precaution, it’s best to back up your data before
  creating new partitions on your device.
  
  Add a volume to a device without erasing existing data
  
  
  Select the device in the sidebar, then click the Partition button .
  
  
  Internal storage devices appear under the Internal section in the
  sidebar. External devices appear under the External section in the
  sidebar.
  
  When you select a volume that already has data on it, the pie chart
  shows a shaded area representing the amount of data on the volume and
  an unshaded area representing the amount of free space available for
  another volume. Disk Utility also reports whether the volume can be
  removed or resized.
  
  If you see a small volume with an asterisk, the partition is smaller
  than can be represented at the correct scale in the chart.
  
  
  Click the Add button .
  
  
  Disk Utility splits the volume into two, leaving the data in one
  volume, and creating a new, empty volume. If the existing volume is
  less than half-full, Disk Utility creates two volume of equal size.
  Otherwise, it creates one volume large enough for the existing data,
  and another volume with the remaining space. Depending on the space
  available, you can create multiple volumes by selecting the new
  partition, then clicking the Add button ![enter image description
  here]3.
  
  
  Click each volume in the pie chart on the left, then enter a name for it.
  
  
  For MS-DOS (FAT) and ExFAT volumes, the name must be eleven characters
  or less.
  
  
  Enter the size or drag the divider to increase or decrease the size of each volume.
  For each volume, click the Format pop-up menu, then choose a format.
  
  
  Mac OS Extended (Journaled): Uses the Mac format (Journaled HFS Plus) to protect the integrity of the hierarchical file system.
  Mac OS Extended (Journaled, Encrypted): Uses the Mac format, requires a password, and encrypts the partition.
  Mac OS Extended (Case-sensitive, Journaled): Uses the Mac format and is case sensitive to file and folder names. For example, folders named
  “Homework” and “HOMEWORK” are two different folders.
  Mac OS Extended (Case-sensitive, Journaled, Encrypted): Uses the Mac format, is case sensitive to folder names, requires a password, and
  encrypts the volume.
  MS-DOS (FAT): Use for Windows volumes that are 32 GB or less.
  ExFAT: Use for Windows volumes that are over 32 GB.
  
  Click Apply.
  
  
  Click Show Details to view the step-by-step process of creating a new
  volume.
  
  
  When Disk Utility is finished creating the volumes, click Done.
  
  
  After you partition a storage device, an icon for each volume appears
  in both the Disk Utility sidebar and the Finder sidebar.
  
  Enlarge a volume If you have multiple volumes on a device and one of
  them is running out of space, you may be able to enlarge it without
  losing any of the files on it.
  
  To enlarge a volume, you must delete the volume that comes after it on
  the device, then move the end point of the volume you want to enlarge
  into the freed space. You can’t enlarge the last volume on a device.
  
  WARNING: When you delete a volume, all data on it is erased. Be sure
  to back up your data before you begin.
  
  
  In the sidebar, select the device that contains the volume you want to enlarge, then click the Partition button ![enter image description
  here]3.
  In the pie chart on the left, select the volume you want to remove, then click the Remove button .
  Click Apply.
  
  The volume is removed, reformatted, and all free space is assigned to
  the previous volume.
  Click Done.
  
  
  Erase and repartition a device You can erase all volumes on a device
  and create new ones. For example, if you want to change the partition
  map of a USB, Thunderbolt, or other storage device from Master Boot
  Record to GUID Partition Map. If you simply want to erase a volume,
  see Erase a
  volume.
  
  WARNING: Erasing and partitioning a device destroys all data on all
  volumes of the device.
  
  
  Select the device in the sidebar you want to erase and repartition, then click the Erase
  button.
  
  
  Note: You can’t erase the device that contains your startup volume.
  
  
  Enter a name for the initial volume.
  Click the Map pop-up menu, then choose a format for the initial partition.
  
  
  For MS-DOS and ExFAT partitions, the name must be eleven characters or
  less.
  
  
  GUID Partition Map: Used for all Intel-based Mac computers.
  Master Boot Record: Used for Windows partitions that will be formatted as MS-DOS (FAT) or ExFAT.
  Apple Partition Map: Used for compatibility with older PowerPC-based Mac computers.
  
  
  Click Erase, then click Done.