Below is an easy step of how to delete a hard drive partition on a mac you can try.
How to delete a hard drive partition on a Mac easily
Step 1: Erase partition.
Open Disk Utility (Applications > Utilities). Click the partition you want to delete in the left panel. After selecting the partition, click Erase button at the top of Disk Utility. Erase button window will come up, click erase and then click done.
Step 2: Remove partition.
You still need to delete the now-empty partition in order to reallocate its space to the rest of your hard drive. Select your hard drive from the left panel and click the Partition button. Click the “-” button and then click Apply.
After a minute, Disk Utility will finish applying changes your drive. Click Done to complete it.