the dash speakers are a B*TCH but you'll need an offset screwdriver...there cheap or option 2, if you can find one of those flexible screwdrivers that will make your job so much easier, from there just unscrew and remove, be very carefull not to damage the dash or the speaker grilles, they brreak easy, IMO if your speakers are shot i would disconnect the wires and leave them there since they suck anyway, dixie monte carlo has door panels thats take a 6" and put some small tweeters on the dash they use double sided tape so no breakage there.
After taking a breath if you dash is looks like crap already then put what ever you want in it, keep in mind those speaker in the front are that size only, so any larger upgrades are a no no...
rear speakers that should screw right out...
step 1. open trunk
step 2. get in trunk and position yourself close the the rear deck and look up (should see speakers)
step 3. unscrew.
step 4. drink some beer and say wtf was GM thinking using the bottom of barrel AC Delco's