Depends on how dry it is ( a few needles falling off or piles of needles on the floor?)
Since it's already decorated you might try boring some holes in the trunk, well below the water line, so that you don't have to handle the tree too much.
Unplug the tree, then using a turkey baster, remove the water.
If it already is, or gets very dry I'm afraid all you can do is get rid of it. Pain, I know.
It may now be a fire hazard although the little cool lights today are much safer today than the old larger ones.
Still, spontaneous combustion does happen!
If you should ever decide to get an artificial tree just hang a wreath in the room with the tree 1 or 2 days before Christmas (they will be really inexpensive then too!) and you will still get a little of that wonderful aroma.
I've heard of (and tried some) many suggestions, ) aspirin, sugar, etc.but unfortunately I have never known any of them to work.
Good luck!