There are two screws, most likely phillips head, that hold the bottom of the sign in, you can access them by looking under the selection panel with the coin door open. They are tough to get to but the selection panel pulls forward some to allow access. Then the sign pull out from the bottom first as there are two pegs in the top.
If you have a Coinco mech, here are the instructions on setting the price:
http://soda-machines.com/discussions/index.php/topic,1138.0.htmlIf it's not a Coinco, then either post a photo or model # of the coin mechanism.