Administrator gone and no Admin password

MS SBS 4.53. The person that originally configured this network has left the area from what I can ascertain. The customer has 1 server and 4 PC’s. Everything is functioning correctly from what we understand. The problem is they are moving to a new location and want us to transport and re-setup the network. Is there a way to add a user with Administrator rights, find out the password or is there a backdoor into the system? Any help would be appreciated. I have heard of apps that can read a password but The console is locked and we can’t get in. Any help would be appreciated.
Gale Joy