Rust on the Window Frame

[four-eyed stang]

I finally found some rust on the 81 I just bought. It is on the passsenger side window frame between the lip and the inside edge. I have no clue how water collected there because it is on the downward slope heading toward the door hinges. The area is pitted but has not rusted thru. What do I need to do to the metal to neutralize the rust before it spreads?