First, your set must allow programming (or use another programming-capable set in the system); these are 7310s or the 24-button model.
Next, you need Admin or Installer programming access, which is password controlled. Check with your phone person. Try using the default PW of ADMIN. Enter this twice (yes, twice). Navigate in the main menu thru "Terminals -->your extension number, to Name. Follow the on-screen prompts.
Manuals can be downloaded from various Norstar vendor web sites.
Best
Mike