Unfortunately, I agree with a lot of the people saying "This may be beyond what you can safely DIY." I have an elm that needs trimming, and I need to get quotes. I'm entirely comfortable with a chainsaw and boom lift, but there is a LOT that can go wrong with trees (especially elms, they're assholes of the tree family with how they like to drop branches without warning) and trimming them.
It is probably wise to pay someone who knows what they're doing, has the proper equipment, and is a licensed/bonded sort of business for large scale tree work. To make things more interesting, mine is near enough to some rather high voltage power lines that I wouldn't want to work on the "easy" side of it.
I'm quite comfortable with a chainsaw, including on ladders, but 30-40' in the air, around power lines, over uneven ground, exceeds my comfort level by a lot. :/