Archive - Is essentially deleting a user and revoking their access, except it preserves their data and interactions. Permanent deletion will remove all data and is highly not recommended.

To archive a User, go to Setup > Users.

Select Archive under Options. 

NOTE: Archived Users can be viewed by selecting Include Archived Users check box

To update records tied to this user with another user, select new user as Primary Counselor. Also, select new user to reassign User's incomplete followups.