Its a piece of cake.
All you need is a drum key. Loosen and remove each tension rod on one head. The RIM will easily come off at that point. Remove the Rim and head. Do every thing in reverse order...... done.
When you put the tension rods back on the drum, get them all on loose, then tighten each one finger tight around the drum, just to snug it up to the rim. Once that is done, take the key, and give 3/4 of a turn on each rod around the drum. And that will tighten the head, and might even be close to a decent sound.
Tuning isn't that easy, but the general idea is what you are after.
I assume your djembe had a goat skin or other hide head... those do not do well with sun. The heat tightens up the head to unbelievable proportions. Mylar drumheads will not do that. Straight up sun is not good for the drum covering though. Stacking the drums until you make a decision on a sale probably wont hurt anything.