I judt did the same thing on my 300ex, and it's the same design. First off, get a manual. Pull the wheels off, hubs, loosen axle nuts. The sprocket comes of last: you'll need the engine/trans resistance to torque the nuts off. Take off the brake caliper, and you may need to loosen the skidplate. Take off the rear sprocket. Slide the axle out of the bearing housing. You'll need to loosen up the 2 hex bolts (normally loosened to tighten the chain)to get the bearing carrier out. Pop out the axle seals and bearings. Clean everything before reinstalling. Put the new bearings in, you can use the old ones to sink them all the way in. Since steel bearings have a tendency to spin on the aluminum housing, you can put a REAL thin layer of Loctite in between. Make sure the spacer in in there. Put seals in, and new 0-rings. Put back together as disassembled. Proper torques are in the manual. Although the bearings are sealed, I greased the hell out of mine anyways. The only real tricky part (and it's really not) is the double-nut on the brake disc. It's got a reverse thread on one part.

 

How is the best way to remove the rear axle from an Honda 250X so I can install new Axle bearings