Start by adding some mild acid to the bolts (for example vinegar and water solution). Let this soak for a while then use a fine steel wool to rub off the rust. Also add oil to try and loosen the bolts after most of the rust is off.
Well for stubborn rusted bolts it's always a good idea to soak them in advance with some quality penetrating oil. After they have it sets for awhile you can try to break them free again. If possible you can try adding a little heat to loosen them.