A hand held impact driver will usually remove the slotted screws holding the drums in place. These are available from Harbor Freight at a modest price.
On the occasions when my impact driver will not remove the screws, I use the large flat screw driver bit and 1/2" socket adapter from the impact driver to install it on my 1/2" electric impact wrench. So far this set up has never failed to remove the screws.
Of course once you have the screws removed the drums may be rusted to the axles. If so, GOOD penetrating oil, finese, and patience will usually get them off. Be sure to back off the brakes before trying.