airbrush_assasin

Heat gun and a long drift. Put the new bearing in the fridge while your getting the old one out, and heat the headstock to re-fit it. it will give you time to give it a few good whacks with a hammer. Use a large socket to hammer the race in. Getting the bearing off the stem requires heat again, use a chisel and tap it with a hammer round the base, be careful not to go too far and damage the stem. refitting new one needs more heat, get a tube that is slightly bigger than the stem but same size as the bearing and tap it down till it stops.
to hold the bike get a paddock stand and 2 axle stands and support under the motor or either side of the frame. good luck. There are bearing removal tools available, just search the net.