Dryer makes a load squeaking noise while running.
The most likely cause for the unit to be making a squeaking noise would be a bad rear bearing. You will want to check to make sure that the felt around the drum to make sure that it is not damaged.
how do you get the top off .
To remove the top on your unit, there will be 2 or 3 screws on the back of the unit that you would need to remove the slide the top backwards.
Squeaks while running, front of drum sagging and clothes come out with brown streaks on them. Do I need rear bearing as well as front glides?
It would not be a bad idea to replace the rear bearing at the same time that you replace the slides as the bearings can be damaged when the slides are bad or missing.