I don't want to lose the pounds, according to my BMI I am 19.5, just barley over underweight. But, according to my BFI, I am risk of obiesity. I dont wnat to starve my self to get skinny. I also dont want to be like a twig

What I am:
Thighs: 20 inches
Abs: 26
Butt:35
Chest:31
Hips:31
Stomach:30

What I want in 3 months:
Thighs: 18
Abs: 24
Butt: 30
Chest: 28
Hips: 27
Stomach: 28

My question:

1) What are some helpful exercises I can do at my desk and floor

2) Ive heard that you can't target one specific area... is that true?

3) Is running the only way to lose the inches?

4) What can I do to lose those inches and how much and how often?

(I can't go to a gym, but I have a weight set and a treadmill at home)

I want to be in shape for summer.... help please!!!!