Failing that, if you look closely inside you can see the screws you need to remove. If you do a search on here I think there's a post on recovering a lonestar grill and how to remove the front.
I've found it:
"To replace grill...you must remove all the screws holding the grill baffle to the speaker baffle. To do this you must remove the rear panels (from the back of amp) to acces the screws. I seem to remember there being about 9 or 10 black phillips head screws holding it on. But look carefully...as the screw heads blend in really well with the black that the speaker baffle is painted. After you remove all these screws you can remove the grill baffle from the speaker baffle from the front."