Not only does PgAccess allow you to modify and view elements of your database, it also provides the ability to graphically modify and manage user accounts associated with the database. This feature is available through the Users tab on the left side of the PgAccess window.
Clicking on Users will display a list of all users associated with the database. Of the program's three action buttons, only New and Design perform any action from this tab.
Clicking New will allow you to create a new user within the database. There are various options in the "Define new user" window that correlate with options available within the command line interface, such as the options to allow a user to create databases and create other users (both of these are check box options within the window), as well as set a date the account is active until.
Clicking Design will allow you to modify the user attributes of any user in the list via a window that looks exactly like the "Define new user" window. Hence, you can change the username, password, the allowed actions, and the "valid until" date.