You can do these things from your user cp. There is a link on the upper nav bar but here's a direct link:
http://www.montanaowners.com/forums/usercp.php
Look over to the left for various options to change up your account.
You can add an avatar image (display next to posts) and also add a profile pic (to display on your profile page). be sure to scroll down and hit save after making updates.
here is a thread that details the specifics of how to do these functions:
http://www.montanaowners.com/forums/...ad.php?t=70323