You can. If somebody is no longer using your computer, you can delete that user's account.
You needto delete user accounts.
Type "Settings" into the global search bar on your desktop. Click on the resulting Settings icon, or press Enter, to open.
Click on Users.
Press Unlock in the top right corner and type in your password when prompted.
Select the user that you want to delete and press the - button, below the list of accounts on the left, to delete that user account.
Each user has their own home folder for their files and settings. You can choose to keep or delete the user's home folder. Click Delete Files if you're sure they won't be used anymore and you need to free up disk space. These files are permanently deleted. They cannot be recovered. You may want to back up the files to an external drive or CD before deleting them.