Assuming all DT300i are the same:
1. Remove muffler by loosening slip clamp at forward end, removing three bolts in the middle of muffler, slide to rear.
2. Remove seat and tub ( to gain access to upper right rear shock absorber/spring assembly). Remove upper and lower bolts on shock, then remove shock.
3. Remove rear brake caliper BUT LEAVE HOSE CONNECTED! Dangle or hang caliper out of way.
4. Remove rear tire "huggy" fender.
5. Remove swing arm cast plate by removing two bolts at forward end and big nut on axle. Note the spacers sizes and locations. This will be normally the most aggravating, frustrating part of the project! The bearing must slide off the rear axle shaft and the rust will lock it on the shaft. Only light rust but the clearance is small. Lube the shaft liberally with your favorite light oil, WD-40, penetrating oil, whatever and pull, pry and cuss it STRAIGHT OFF. The first removal is the worst. There is no puller that will grab that plate evenly so don't bother. I have used the puller legs as prybars successfully.
6. Remove wheel. PITA, ain't it!