Don't know how to replace AA batteries in Maglite AA.

Some lights have a slot, (for lack of a better explination) in the back end. Get one of those rubber jar openers and use it to hold the light while you insert a small screwdriver shaft through the slot. Use the screwdriver for leverage. It may help to give the threads a shot of wd40 beforehand.

They either unscrew from the back end or they unscrew from around the thick light end , then just pop in some new batteries making sure that they are pointed in the same direction