Easy! Begin by clicking your initials or photo avatar in the top right corner and selecting the Users option from the dropdown menu.

Click on the row of the user that you want to delete. On the bottom under the "Permissions & Actions", click on "Delete User".

Anow will ask for confirmation to delete this user. Click "Delete User" if you're sure.

All files they were associated with will remain with their name in tact for your records. However, they will no longer be able to login, and you can no longer assign them to any files.