How do you change the oil on a 2002 Yamaha ttr 225?

Well, I have an '04 TTR225 and I'm sure they're quite similar. On the lower left side of the engine, directly behind the gear shifter, there will be the oil plug. Loosen it with a 19mm wratchet. The oil will immediately begin to pout out. Contain it somehow with a bucket or whatever is available and dispose of it accordingly. Then reinsert the plug and fill it with the correct amount of oil. The entry wat for the oil will be directly above the "YAMAHA" logo on the right side of the engine casing. Pop that off and fill with the correct amount of oil. And there ya go(: