your gonna have to remove the rear fender and use a pry bar but youll be able to pry that back up using the meat of the frame ahead of it. Every action has an opposite and equal reaction. So if its bent to the left and down come up from underneath and go to a section of frame on the left above the swingarm bolt somewhere and pry up. Your gonna have to hold the bike down somehow to really get at it. I had my brother sit on the rear tire and tried and it wasn't enough. I tore mine down to paint the frame and I had bolted it with wood blocks to the bed of my truck and strapped my bent point to a tree and slowly let the truck weight bring it back to shape. (hillbilly porta ram)
Frame chained to floor and wood block and jack is another way. Anyway you look at it .....it can be done. Most you have to remember is go slow and move it incrementally till its right. Watch for stress cracks and if need be remove more plastic to use heat etc.
If you cant fix it with a hammer, you have an electrical problem.
Funny, my KDX looked like that when I bought it. It was really my first bike so I didnt know that it was abused or anything previously. I was riding the other day and that bend snapped. Right where the muffler mount connects to the frame. I agree with everyone saying to watch for stress cracks. Once mine snapped, you could see how deep it was cracked before and then where the fresh crack happened. Im going to weld my frame back together when I can!