How do you check the hydraulic pressure for the convertible top of a 93 Cutlass Supreme and how do you increase the pressure or refill the fluid?

you will have to remove the rear seat as the pump is located behind the backrest. To remove the back seat, you need an extension for your socket wrench and remove the two nuts which are about centered where each person sits. Then lift up the seat to clear four guide/retaining clips.
Having done that, next lift the cloth well that is glued to the top edge. Now you can see the pump/motor. it will have clear hydraullic lines on both sides and a electrical connection. There is a rubber plug on the side. Turn pump so this faces up. You will need about 2' of rubber hose or a funnel and a coffee can 1/2 full of trans fluid. Pull out the plug and insert hose from can to pump.run top up and down a couple times. This will fill and bleed the air out. You may need to do this 8-10 times. Don't let the motor get hot--it's not made to go more than a couple times without cooling off. Replace plug and inspect lines for leaks.
I have a 95 cutlass supreme, and the pump is visible and accessible from the trunk. Just lift up the cloth bag that the top folds into and you will see it. It is a long reach through the trunk. My plug was on top of the unit, so I did not have to remove the unit; just unplug and refill.