Trouble with my partitions
The problem is that the Yo volume is inside a CoreStorage logical volume group. You can manipulate them from the command line, but the easiest thing to do is just revert it to a normal partition (in the terminal):
diskutil coreStorage revert /dev/disk1
This shouldn't cause data loss, but as always when working with partitions, back up anything you can't afford to lose. Once it's a normal partition, you should be able to manipulate it in Disk Utility again.
See man diskutil for more information.