Thanks, both out but looking for wiring more than anything else as I can't see where the tweeters connect to the main speaker
Speaker loom is in the door. If you're going to change the speakers then unplug the tweeter connector and tape it up out of the way - you won't need to use it again assuming you're fitting new components with a crossover. Remove the connector to the driver in the door, leave a few cm of cable with the plug and cut the wires. You can then use these as the input cables to the new crossover that should come with your new speakers. There's a space behind the door card where the crossover will fit neatly without getting in the way of anything. It'll just wedge in there and shouldn't rattle, but you may want to secure it. Run new cables to the new driver and up to the new tweeter.
The space for the drivers is quite shallow, many aftermarket speakers won't fit as a result. There are a few decent speakers around that will fit, though. I have Focals in my GS and they're very good. The standard tweeter can be removed from the grille/holder by turning it through about 90 degrees and pulling out. You can now fit the new tweeter in its place with hot glue or whatever you prefer.