its very easy, just changed the deck in my '03 wrx wagon:
1)open cupholder above it, remove 2 phillips screws
2)put out the whole cupholder/blank plate assembly unit next to it
3)the trim bezel is held on by 4 clips -- 1 on each side towards the top, 2 on the bottom. start from the top on either side and take your time not to snap the bezel. you'll be able to tell where the clips are. once you get the top 2, the bottom 2 come out pretty easily
4)that's it, you'll now see that the oem deck is fastened by 6 more phillips screw - 3 per side.
hope this helps, i don't have any pics but it really is easy once you get going.