Strategies To Lose Weight Fast

So my friend and I are wanting to lose 10 pounds safely. I would definitely say it’s our last 10 pounds that we need to lose. So I was wondering how we can do this safely, and make sure that it stays off. Okay, thanks !
By the way, we’re 13 and 5’7. I have soccer practices tuesday and thursday for an hour and a half, and then a game on sunday for hour and a half. But my friend does not. We plan on starting to go to the gym 2 times a week.