Since I have done this instructable, I have made diagrams on how to use a socket to switch out crystals and how to use a switch to change speeds. Those diagrams can be found here http://forums.modretro.com/viewtopic.php?f=40&t=114
Step 1: Tools needed
soldering iron (30- 40 watts is fine)
crystal (14mhz or 16mhz is recommended
triwing screwdriver or small flathead screwdriver
basic soldering skills
a game boy color (duh)
rosin core solder
Step 2: Taking it apart
However, if you do not want to spend 5 bucks, you can use one of those mini flathead screwdrivers. The trick is to put the tip inbetween the three intersections on the screws. Then, if you did it right, can take out the screws.
Now, after you have the case off, you can get to the insides. There are screws atatched to the board, but we do not need to take these off.
Step 3: Locating and removing the old crystal
To remove the crystal, get a small pair of vice grips, and clamp the crystal with it. Move the vice grips back and forth, and, if done correctly, the crystal will come off. Be careful not to break off any surounding parts though. Now there should be some visible contacts where the crystal was attatched. This is where we will solder the new one to.