Start the agent GUI and then select Tools/Options menu. Click the Service tab and choose to run it as a service, make sure to check the Agent box if you want 24x7 to run in the agent mode. Enter account name and password. Quict the agent and start the configured service.
After this initial setup you can alsways change account and password directly in the control Panel using the services applet.

PS. It might actually be easy to set the agent running under an admin account whose password never expires and run remote jobs as another user.

: We have the agent running with an account rght now and we change the password
: every 40 days, but I want to set it to run as a service, I am sure that it
: is in the docs, but I thought I would ask the Q while I am going through
: the doc and maybe this would be faster. Thanks