I did this in my old 1992. Actually go to a salvage yard and get some matching panels from a newer Bonneville or one with the upgraded system. that way you have a wider selection for speakers (5-1/4"), plus you'll have tweeters (factory pre-wired, you just have to plug in). If you aren't up to that here are the directions for removing the door panels:
Tools you need are : T15 torx bit screw driver, medium philips screw driver, and medium flat screw driver, ratchet, and a small socket (can't remember size, but around 1/4").
1. Take the cap out of behind the door handle using a flat screw driver to pop it out.
2. unscrew door handle trim ring with T15 torx bit.
3. use flat screw driver again to remove the trim piece at top of the grab handle (houses the mirror controls on drivers door), popping it off with the screw-driver going into the front of it (it hinges out from the back then. Unplug mirror controls and light.
4. Use philips bit screw driver to remove screw.
5. remove the door light at the middle of the back of the door panel. Do so by pushing the flat screw driver into the back end and pull the handle back so the tip moves forward and out with that end of the light. Once that end it out pull it out and unhook the light. (carefull as these lights are very fragile).
6. Use philips screw driver to remove the two screws behind the light.
7. Use ratchet and small socket to remove the two screws at the front of the lower panel that houses the speakers.
8. Use meduim to large size flat screw driver and go around the edge of the door panel, putting it between the door panel and the door and turn it away and the tilt the screw driver until the "pin'*" pop out of the door.
9. After the pin'* are free'd lift straight up gently on the door panel working from the back to the front so as not to break the black plastic strip that goes across at the top of the panel as it is one long hook.
10. When that is off rest the panel on something about the same height as the bottom of the door and unplug the power windows, locks, and speakers.
11. Use small phillips screw driver and remove the door panel pocket from the door panel. There are about 8 screws if I remember correctly.
Also be sure to get some speaker wire adapter'* at Best Buy or an audio store so you can put the stock speakers back in if needed without resplicing the connections.
Hope this helps,