Expose the truss by pulling the shingles and boards back from the roof using a crowbar.
Locate the metal plates on the truss. Typically you remove and replace one plate at a time as to maintain the integrity of the truss.
Unfasten all the screws holding the metal plate to the truss with the drill. Try to not strip the holes in the wood; if you do, you will need to put anchors in the wood in order to reattach the metal plate.
Replace the plate with a new plate, lining the holes for the screws up with the former holes. Replacement usually happens if there has been rusting or damage to the plate itself.
Repeat the steps if you need to replace additional plates. If you need to remove the truss altogether, be sure to add supports to one side to secure the truss in place.
Replace the boards and shingles removed from the roof once you are done working with the trusses. Attach as the pieces were put together before, usually with a nail gun.