How to cut off an old swing to get rid of it
You have numerous options:


Drill out the screws with a drill bit larger than the screw diameter.
Use a hand hack saw to cut it into manageable pieces.
Use a reciprocating saw - a "Sawzall" to cut it into manageable pieces.
Beat it into submission with a sledge hammer until it folds and bends and breaks (get medieval on it!)


My recommendation would be the sawzall with a new 10" demolition blade. You can probably have it cut into pieces in 10 minutes that way with little sweat.

If you don't own a recipricating saw, you can rent one at your local tool rental place or big box hardware store (Lowes, Menards, Home Depot, etc)

edit: Like SteveR says...make sure to wear your safety gear!