You certainly can. All it takes is:
Locating Disk Utility in Finder > Applications > Utilities. You can also search for it on Spotlight via the menu bar or by pressing Command + Space heading to Disk Utility.
Clicking Partition.
Selecting the partition you want to delete from the pie chart and clicking the delete button (–).
Clicking Apply and then clicking Partition.
Always back up your data before you begin, as all data on that partition will be erased.