how can i thin my already muscularly big thighs?

Answer 1

When I lost muscle on my thighs it was because I stopped working out and ate less. But it took me many months to lose what I built up. Less excercise and less eating can cause the muscles to atrophy, or become cannibalized by the body when it needs protein and you aren't supplying it with enough in the foods you eat.

Answer 2

I don't think you can unless you're willing to lose muscle mass and trade it for lean muscle. If you squat 250 you should squat fewer pounds and do more reps, the same, perhaps fewer; run and stretch instead.