You should be able to adjust the roller height by accessing an adjustment screw through a hole at the sides/ends of the bottom frame piece.
Spray the adjustment screw assemblies with penetrating oil then lower the door completely by backing out (loosening) the adjustment screws; then lift the door up into the upper track and swing inward to remove it. Be careful, they are heavy; for wider sliders this is a 2-man job.
Lay it flat on sawhorses and inspect the roller mechanism for damage/wear. Spray the entire roller assembly on each side with penetrating oil then remove the rollers, they are usually removed by removing an additional screw found on the bottom of the door frame near the corners. Replace if worn or damaged, if not, grease the wheel bearings with a small amount of lightweight multi-purpose grease and reinstall.
Check all weatherstripping felt and replace as necessary. Spray the entire upper track area with spray silicone lubricant, no other type of lubricant will work as well. Check the rail that the rollers ride on, if it is damaged or corroded as to make sliding difficult, it can be repaired with a "crimp on" stainless steel track cap.
Clean entire door frame and entire track frame, using shop vac if necessary to remove all dirt and debris. Make sure wheels are set to their lowest height adjustment then reinstall the door by reversing removal steps. Adjust the door height until door rolls smoothly and is plumb at the frame on the latch side and aligned with the latch catch. Most latch catches can be adjusted slightly if necessary.
below pic is an example, there are many, many types: