Below is photographic instructions for how to install the shim and Thudbuster seatpost. The reason for needing to do this is that the Thudbuster seatpost is a slightly different diameter post to the post supplied with the bike.
You'll need a 2MM Allen wrench, a pair of pliers, a flat head screw driver, and a hammer.
Undo quick release, and remove original seat post if installed.
Use the 2MM Allen wrench to loosen this screw, then gently twist off the seat post collar.
Use pliers to pull the old shim out. If it's a bit stuck, use the flat head screwdriver to tap the shim up and out of the seat tube.
Insert the replacement shim.
Replace the seat post collar and tighten the 2MM Allen screw back down. Don't go too tight, just enough so the collar won't spin easily.
Insert your Thudbuster seat post, make sure you can't see the Min Insertion Line above the collar, then adjust your saddle height and close the quick-release on the collar. All set and ready to ride!
Note: Probably wise to keep the old shim taped to the old seat post, just in case you want to go back to a standard seat post at some point.