The first step to disassembling the drum brakes is to go to the "general support" section of this forum and download the downloadable manual which will cover all of these steps in detail.
Just for reference, I'll give you the run-down: First, jack up the quad and remove the wheel.
Then you should loosen the brake cable and remove it from the backer plate.
Remove the cotter pin and the nut from the outside of the drum.
Pull the entire drum off the end of the spindle. If the brakes are REALLY bad, you'll probably need to forcibly remove the drum from the backer plate (which is why I tell you to remove the cable so the backer plate will come off with the drum if they are rusted together).
Once the drum and backer plate are no long together, you'll need to check the inside diameter of the drum and for straightness.
Remove the two shoes.
Remove the 6mm bolt out of the brake cam arm (on the back of the backer plate) and remove the arm from the cam shaft.
Drive the shaft out the front of the backer plate.
Grease the cam shaft, seal, and shoe pads with white lithium grease.
Check the bearings inside the drum and reinstall making sure to tension the nut on the outside and reinstall the cotter pin.