Change account used for networker

Hi, I have to delete builtin\administrators login from sql server. One of this administrators is networker_sql windows user which runs backups. I created new windows login networker_sql as sysadmin server role in sql server, and reduced builtin\administrators from sysadmin to public server role. Now, when I hit button NetWorker Backups in SSMS I cannot see list of available databases. I cannot figure out, what Im missing. When I change builtin\administrators back to sysadmin or even serveradmin server role, I can see the list. Looks like networker_sql is still connecting to sql server using builtin\administrators and not new windows login. How to setup networker account properly?