Chandeliers are made to come apart and go back together. There are two issues here, one being how to disassemble the chandelier and the other is how to get yourself up there to do it.

This is how I go about reaching stuff in my house that is high up and far away from a wall. I do not recommend this to other people, but it is how I do it: I move a large, sturdy table, like a dining room table, and place it under the chandelier but slightly off to the side. I cover the table top with cardboard. Then I take the largest step ladder I have and place it on the table. I stand on a chair, then stand on the table, then climb the ladder. I know all the things that can go wrong with this, but I have done it a few times, and it works.

As for disassembling it, I suspect that unscrewing the knob at the bottom may release the glass shade. The question is whether the three prongs are also screwed in or just holding slight pressure against the globe.

You might try posting this on the Home Repair forum. The guys there may have a better idea of how to get the globe off.

We go through this, also...

Your very best bet here, is to replace it with something like this...

Or a similar style...no glass shades to clean, nothing to tarnish, nothing to collect bugs.

Use led bulbs so you don't have to change them...

This style requires cleaning from the top because the glass is held in place by the three arms and the bottom nut. A popular method is to snag it from the second level hallway, haul it over to the hallway, clean it, then release it slowly with whatever you used to snag it.

I suggest you replace it with something that does not have any glass and has LED bulbs, as pennydesign says.