To delete a partition, right-click on the partition (smaller rectangle) inside a disk and select Delete partition.
Press OK to confirm your decision.
You can now preview your changes.
Press Apply operations, then – Apply.
After performing this operation, Unallocated space will appear where the partition used to be. You still can restore accidentally deleted partition using Undelete Partition (unless you have Wiped it).
Hard Disk Manager for Mac, HowTos: Mac OS X, Products for Mac OS X
Tags: delete, HDM for Mac, mac, partition