Resizing dual boot partitions in Yosemite
There are at least two approaches to solve your problem:
One is potentially destructive, vastly undocumented and i don't know if it works (1) and the other one is  for sure destructive (2). 

So please backup your Mac OS X and your Ubuntu partition if necessary.

Requirements: USB thumb drive with a full working Mac OS X and iPartition installed or a Linux Live USB with gparted.

It's also useful to have a second computer with internet access and the stackexchange credentials to check back if you run into severe problems.

(1) risk of destruction  (this may render your systems unusable):

Your Mac OS X partition (Macintosh HD) visible on the desktop is equivalent to the Logical Volume 4F26F5C3-8D94-419F-AFF1-B652E9DCDEF4. You may shrink it down to the 82.68 GB which will render your OS X almost unusable because it needs some free space. You may disable the sleepimage and gain the amount of your RAM size as additional free space though.  


Restart into Internet Recovery Mode by pressing cmdR
or your bootable Mavericks Thumb Drive with iPartition installed.
start Terminal from the menubar/utilities
enter following command at the Terminal prompt: 



  diskutil cs list
  Copy the Logical Volume (LV) alphanumeric UUID of your CoreStorage volume. The LVUUID should be the fourth listed. In the above example the alphanumeric is:
  4F26F5C3-8D94-419F-AFF1-B652E9DCDEF4.
  Run the following command:  



  diskutil cs resizeStack LVUUID  


According to the number found above it would be:  


  diskutil cs resizeStack 4F26F5C3-8D94-419F-AFF1-B652E9DCDEF4 88g  


This will hopefully shrink your CoreStorage volume to 88 GB (skip to step 9 if this doesn't work)
If necessary reboot into your thumb drive and start iPartition. Alternatively you may use a Linux Live USB with gparted.
Try to move the volume Recovery HD to the end of the now shrinked Macintosh HD  (skip to step 9 if this doesn't work)
Expand your Ubuntu partition


(2) total destruction (this will delete all partitions on your disk)


Disconnect all external hard drives
Restart into Internet Recovery Mode by pressing Command+R
(alternatively you may use a Mavericks or Mountain Lion Install Thumb Drive)
start Terminal from the menubar/utilities
enter following command at the Terminal prompt: 



  diskutil cs list
  Copy the Logical Volume Group (LVG) alphanumeric UUID of your CoreStorage volume. The LVG UUID should be the first listed. In the above example the alphanumeric is:
  08436957-C5CD-4DC6-B9FA-05B51A3EEFC8.
  Run the following command:  



  diskutil cs delete LVGUUID  


According to the number found above it would be:  


  diskutil cs delete 08436957-C5CD-4DC6-B9FA-05B51A3EEFC8 


This will delete your CoreStorage volume and probably your Recovery HD and reformat it as a simple HFS+ volume.
Quit Terminal
In the now opening window choose Disk Utility erase all leftover partitions and format/partition/rename the internal drive. Choose 1 Partition, Mac OS Extended (Journaled) and GUID partition table (available with the option button). Quit Disk Utility.
Now choose 'Reinstall Mac OS X'
The originally shipped OS X will be downloaded and installed or the one provided with the aforementioned OS X Install Thumb Drive.
Set up your Mac
Download and install Mavericks/Yosemite from the App Store if necessary
Install Ubuntu (in a larger partition now)