You aren't able to completely delete a user but you can deactivate a user. Deactivating a user removes their access.
Table of Contents:
Deactivate a user
Navigate to Admin > Users.
Click the users name (link), then scroll down.
Deactivating a user makes a user license available. The only exception is when partners are deactivated (users with a blue P next to their name), since partners do not require a user license.
What happens to the contacts, tasks, opportunities, and notes assigned to a deactivated user?
When you deactivate a user, the completed task is removed. You will be asked only who to assign the Pending tasks to. However, notes are not affected when you deactivate a user.
What happens if I reassign to the wrong user?
Make sure you are assigning tasks to the correct user because once the action is processed there isn't a way to undo. However, you can manually reassign tasks to another user.
Video Walk through
Note: Video has no sound.