The grill cloth on a guitar amplifier can have a surprisingly large effect on the tone of your guitar. Older Marshall amps used a weave cloth that did not allow the full sound of the speaker to escape. Certain frequencies, usually those of higher-pitch notes, get absorbed by this material, thus changing the sound of your guitar. Whether this is good or bad is entirely a matter of preference, but if you are looking to modify the tone of your amp -- or simply to make it look better -- replacing the grill cloth is a good place to start.
Unplug the speakers from the back of the amplifier unit. On most Marshall amps, the speakers are attached with a standard 1/4 inch plug.
Remove any back plates and chassis on your Marshall amplifier. These are usually held in place with regular screws.
Remove the screws on the top, sides and back of the amplifier that are holding the actual amp unit in place. Different models of Marshall amps have slightly different screw locations so search all around the actual amplification piece for any hard-to-find screws.
Remove the amplifier piece from the cabinet. Carefully push the unit from the front of the amplifier until it comes out the back. Be careful not to drop this piece when pushing it through the amp. Set the amplifier unit in a safe place along with the screws.
Unscrew the speaker board -- the section of wood that holds the speaker in place -- from the grill frame. These screws are located in the back cavity of your Marshall amplifier.
Insert a flat-headed screwdriver -- or another flat-headed tool -- underneath a section of one of the plastic corner pieces. Carefully pry each of the rivets out of the amplifier frame. Remove the plastic piece once the rivets are out. Repeat this process for the other seven corner pieces.
Move the wooden sides of the amplifier just enough to allow you to remove the grill frame from the amplifier body. Pull the grill frame out of the amplifier.
Remove all of the staples holding the old cloth in place. Pry them out using a small screwdriver. Remove the old grill cloth.
Pull the new grill cloth over the frame and begin to staple it into place using a staple gun. Make sure the cloth is pulled tight over the front of the wooden grill frame. Cut the excess cloth with a utility knife when you are done.
Reassemble the amplifier. You will have to use a rivet gun to insert new rivets into the amplifier frame.