A jack can stick for several reasons.. The most common is lack of lubrication.
A nother is a stuck solenoid
Now solenoids come in two flavors. ONe has some kind of "Manual release" that you can operate.. Depending on the pump brand you either work a "T" handle. Others You remove a plastic cap and then screw driver it.. Others. DO NOT HAVE a manual release.
once you opreate the manual release (Do both the stuck jack AND the dump valve) You can work it up then put a floor jack under it and pump it up.
Then restore the solenoids to normal. but LUBRICATE before you do anything.
I have one "Sticky" jack.. I'll work it out when I get the rest of the system fixed.