The key is a very sharp knife, and steady hand.
The speakers are 10cm upfront with pop off covers, and 16cm rears, bit mine by getting in the boot.
Quick point to note is that the replacement rear speakers need to be very flat faced to go in the holes! I'd go for 1 way rears and 2 way fronts.
Done this so any questions, just ask.
Oh, the rear speaker wires need to check for polarity the strip on one side is +ve and on the other the striped wire is -ve, can't remember which though.