Could be that one of the upper rollers has jumped off of it's track. just lift the glass straight up and reposition the rollers back on the track. if the rollers are on the track then probably the upper rollers need adjusting. lift the door up so the rollers clear the track and remove the whole door. Now with the door off you can see if there is an adjusting screw, some rollers are set in a diagonal slot and you loosen the screw, slide the roller up or down the slot and get them both at equal distances, tighten the screw and rehang the door. Google "adjusting a shower door" and you will get a lot of results. Like this one
adjust shower door
Othertonka
2004 Southwind 32VS 8.1 Workhorse chassis
2002 CRV Toad
U. S. Gear Unified brake system
Retired Fire Captain, SFD