There are two hoses attached to the frame with a clamp just on the inside of the side stand. Use pliers to remove the hose clamps and drain both into a pan. If your oil is in any condition close to how mine was when I bought it, you'll see white sludge coming out of one of the hoses. If that's the case, you might be well off doing a flush of your oil by putting in some 20w50 and running it for a good fifteen minutes and then emptying that out and starting fresh with new oil and a filter.
As for how much, my Buell manual told me 1.5 quarts but in reality it was closer to two. Keep in mind not to fill it all the way up cold; the proper way to check the oil level is a "hot check" after running the bike for around ten minutes.