When a user has left and you have moved all the properties in their portfolio to a new person, you can archive the User - they must have a date in the date ended field.
To move all the properties - go to System Settings - the last tab is called Tools. In there you will find "Change User Assignment", click on Change Assignment. It will ask you who the old user is and who you want to move the properties over to.
Then click on Save changes. This will move all properties and inspections etc over to the new user.
Once you have finished. Save out of there and go back to the user, click on the drop-down next to the edit button and choose to archive the user.