As far as i know, it's just a standard brake drum and shoes type of setup, just like older cars. Once you take the wheel off of the tractor, the drum pulls straight off. It may be stuck from years of rust and dirt, plus there may be a rim of crud built up on the rim of the drum that won't let it go past the shoes easily. You can use the star wheel to adjust the shoes in to their loosest configuration to make it easier. Repeated heating and beating may be required if it's really stuck.
If you want to look at a parts diagram, go to the New Holland Parts lookup website (Click Here) and then type in 2000 into the model number and click the Search button. The 3 cylinder 2000 AG tractor will be the 7th item in the list returned from the search. Click on the plus sign next to "2000 SERIES 3 CYL TRACTOR" and then click the plus sign next to "Brakes" and then click on "02A01 BRAKES & BRAKE CONTROLS...". Once the diagram is up,you can click the "+" button at the top of the picture to zoom in and then you can use the scroll bars to pan around the zoomed picture.