When vehicles are parked over extended period of time, the disc might stick to the flywheel and if this is the problem that you are facing, try the following.
Ensure parking brakes and foot brakes are applied. Chock the wheels if possible.
Engage 1st gear.
Depress clutch pedal.
Crank engine intermittently to kick the clutch disc free. This might take a few tries to get the clutch to release. Be careful as the engine might start and since you are engaged in gear, vehicle might surge forward.
When clutch disc releases, there mght be a loud noise so be prepared and do not be alarmed.