Hi,
EPESI implements lazy delete, so it's not possible to permanently delete a record from GUI. If you'd like to make full clean up then install again.
You should never delete a user (but you can change it's login to something else), because it may cause bugs. Every record has it's owner and even if the user has been "deleted" (deactivated), we want to know that he/she has created that record.
Proper way to deactivate (kind of remove) user.
1. Go to Admin -> Manage users
2. Edit -> change login if you'd like to release it's name
3. Back to the list -> deactivate user with green dot. (without this step user will be still able to login even if you do 4.)
4. Now you can delete a contact. (what really marks this record as inactive - you can restore it from the RecordBrowser admin)
5. Create a new user (with the same login if you wish - but it'll have other id number)