A search would reveal a lot of threads on this topic. You have to take the front wheel off, leave the hub connected to the rim, it will be easier. Pry the rubber seals out on each side with a screwdriver, then spray the bearrings down with a good penetrating oil. A little heat, even from a propane tourch, to the outside of the hub near the bearrings helps as well. Use a long punch, slide it into the hub, and tap the bearing out from the inside. You have to feel for the lip on the bearring, and try to tap it out evenly, working top, bottom, etc. Good luck!
THE 80's RAGE! Currently owns:
81, 85 Yamaha Tri Moto 125
83 Yamaha Tri Moto 200 x2
82,83 Yamaha Tri Moto 175 project
85 Yamaha Tri Z 250
84 Kawasaki Tecate 250
84 Honda ATC 70
85 Honda ATC 350X
84 Honda ATC 250R
(2) 84 Honda ATC 200x
82, 83 Honda ATC 185s
81 ATC 200
Lots of other parts and bikes