I assume you are working from the instructions from the Heartland Owners Library for Lippert Hydraulic Slides dated 2016, and have the slide support arm nuts only LOOSENED. If I were you and could not move the slide with either enough human power or a prybar, I might try turning off the hydraulic pressure to all of the other slides then pulsing the slide in/out power switch appropriately to move the slide as needed.
While you are doing this job, you might want to jack up the slide from the exterior bottom, disassemble the interior lower wood trim on the slide front to inspect the support rollers on the slide. Besides replacing 1 defective support roller I had (which is VERY common with our older rigs), I opted to add an additional J38 roller DIRECTLY UNDER THE CENTER OF THE REFRIGERATOR WEIGHT to better support that weight.
The jacking up and trim removal will give you a couple of inches clearance to remove/replace the roller(s). I had to remove the roller end shaft retainer, remove the shaft and roller to access the screw heads. The old screws may have to be taken out with a right angle close clearance screwdriver ( I found thin nose vice grips a handy help in removing these screws). I installed screws with thin hex heads (thin so they wouldn't catch one the roller) with the hex heads being easy to tighten/remove with an end wrench.