front speakers must be drilled out if they are riveted in. Its easy though, choose a small drill bit just a little larger than the little hole in the centre of the rivet. Drill right through that little hole and the speaker will fall out, disconnect the connector at the back and jobs done. New speaker can be pop rivetted in place or screwed in with screws your choice.
The other way to do the 6x9's is to run the wires all the way to the back of the headunit and in my opinion its easier than having to remove the rear trim.
Remove your head unit and if its and after market with its own loom then it will have marked on the wires which are the rear ones. Cut them and attach you new speaker wires here, feed them down behind the dash down the drivers side is best for speaker wires, lift the door seal and remove the clips holding the carpet down run the wires under here and then lift the rear seat bench off and feed wires under there to the boot.