The hinge pin is held in place with a hex-head set screw accessible from inside the housing. If your meter is an automatic, also remove the rubber boot where the winding crank goes into the back of the housing. Once you have the housing apart, either sand it thoroughly or use some form of chemical stripper to remove the old finish. If you use paint stripper, you'll want to sand everything after removing the old finish. Once that's done, you're ready to repaint.
Aerosol paints are fine.
Just use a good quality paint such as Krylon. You'll get a better final finish if you apply a coat of primer first. I recommend a light grey primer. Once the primer has dried thoroughly, sand it lightly. Several original colors were used over the years including light grey, silver or aluminum, light blue metallic, and a dark grey metallic.