The Techie Side of Disk Utility
From the Volume Scheme list, choose the volume just beneath the one you want to enlarge, and click the – button to delete it.
You can now take advantage of the newly freed space by dragging the divider at the bottom of the partition you are expanding. Alternatively, assign a new size in the box provided. If you have leftover space, click the + button to add a new volume and name it. When you are finished with all this, click Apply.