I would like to know if you are looking to change Printer's admin password or change the local admin password of you HP Server.
If it's a server, you can create your account (Or someone else with domain admin rights) can create you one. Then, you might be able to perform anything without the local admin account.
If you want to change the printer's admin password, you have 2 options.
Remotely on the printer web page by typing the IP address in your browser's address bar. You should have an option, depending the printer's model to setup the admin password.
The other one, kind of pain in the ass is to go directly on the printer and change it manually thru it.
Hope that helped!
Let me know!