I would imagine it is built just like a 4x12, only halved. There are about 6-10 screws on the inside of the cab, around the perimeter, and one or two possibly in between the speakers to connect the middle (where the Mesa badge is). You have to remove these screws (they have black heads, so they are kind of hard to find). Also, once these are removed, if the grille still won't budge, remove one of the speakers from the inside and gently, but firmly, push from behind as well. The Grille will pop out, along with the wooden frame that it is attached to. The piping is attached to this as well. To change the grille clothe, remove the Mesa nameplate, which is just held on by two screws. It can be tricky to remove, because the soft backing on the nameplate can become sort of "glued" to the clothe, even though there is no adhesive used. I just used a knife blade to gently pry it off at an edge. You will then have to remove all of the staples around the perimeter of frame. There are a TON of staples. The staples holding the piping are NOT the staples holding the grille clothe on. These staples are located underneath the piping. Good luck man.
-AJH