The only way to free the caliper up properly is to remove it from the car clamp it in a vise then remove the lever for the hand brake then the rubber seal flood the shaft with some 3in1 oil or similar and put the lever back on and work the lever backwards and forwards untill it is completely free
Wd40 is to dry it won't last , you may free it up on the car but it won't last your brakes will be binding again in no time
Also make sure your cables are free , the calipers are a pain but why by more when you can free them up . Do it right do it once