the mirror speakers?

you reffering to the tweeters??
you could ask someone in the MK 4 section of the forum. but as far as i'm aware...inside mirror covers are either clipped on completely so its just the case of pulling em off carefully....or there may be one screw holding it on..so look out for a screw cap cover that u can prize off wiv a small flat head.
as for the front door speakers, i believe they take 16.5cm / 17cm speakers.
not sure if you have rear speakers but they may be the same size too....i know they are in the MK 3 model, so whether they changed rear speaker sizes in the MK 4 am not entirely sure.