Usually with a stuck clutch the only way way to force it to release is to put the tractor against something like a large tree. Once tight against thr tree, etc put the tractor in a lower gear and let it set there and spin the tires under a load while you push in on the clutch peddle to remove the force of the pressure plate from the clutch disc. IF the clutch is stuck due to the disc being rusted to the flywheel and pressure plate then this usually works, but is not a guaranteed fix. If there is something else wrong that is causing the problem, or the above proceedure doesn't work then "breaking" the tractor to perform a repair is the only way to fix it.
Wayne
November 2009