Step 1. Remove caliper. Check if both caliper pin sleeve bushings wil slide back freely. If not, remove caliper, press out and clean/replace. Also clean mount holes in claqiper. Relubricate with anti-sieze compound and check for smooth movement in caliper. Otherwise proceed to 2
Step 2. As suggested above, use a c-clamp with and old pad and try to press caliper piston back. If the piston will not move back freely, loosen the bleed valve and try again. If it will still not move back, replace caliper. Otherwise proceed to 3.
Step 3. If caliper moves back with the bleed screw loose, there is blockage somewhere in the line acting as a check valve and prventing brake fluid from going back. Often old hoses can do this. Remove brake hose and inspect. If it is rotted out replace. If not continue back up the line til you find the block point. Also check porportioning valve.
If both sides are locking up at the same time, there may be a problem with te propotioning valve. Although if you did brakes recently it may have been something you did with reassembly of the brakes. Did you remove and clean caliper bushings? Did you lube bushing? Did you usea petroleum based grease on bushings (may cause a sieze up). Did you press caliper piston back using a old pad, or with a c-clamp right on the piston (if piston goes back crooked it will jam up)?
Hope this helps get things started for you.