How can you tone up but NOT lose weight?

My thighs have some fat on them, but i think theyre toned underneath.
When i do squats i can see the muscles.
i'm at a healthy weight now (130 pounds, 5'8.5) according to bmi charts.
I don't want to lose weight. I just want to tone my thighs.
The rest of me is well toned, but my thighs are where all my fat goes :/

If the best way is running, how long should i go a day and how long before i see results