How do i lose my belly fat?

I know i can do situps and crunches, but they kill my back. I walk alot, and don’t really eat too much, but I’m like 40 lbs overweight and look pregnant. what else can i do to get rid of this stubborn belly fat?
I’m not just wanting to lose belly fat, its the only place on my body that has fat. I am tall and skinny, but have a huge belly.