How to fix partitions if disk utility is not able to?
You should be able to delete the Windows partition, which will allow you to resize the OS X partition. 

Normally you can simply click on the expansion icon located in the bottom corner of your OS X volume, which allows for easy resizing. However, Disk Utility won't allow this if there is another partition below the one you want to resize:

https://support.apple.com/kb/PH22240


  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.