Honestly at 13 all you'll need is a permanent change in diet. Stop drinking monsters and eating burritos.
As far as exercise goes, at 13 your metabolism is going to take care of just about all you need. If you're looking to get into good physical shape, football/cross country/track will handle that extremely well, plus you'll probably make some new friends in the process. If you're opposed to school sports then any combination of calisthenics and cardio will be fine.
I suppose I don't know much about teens though, I probably wasn't adjusting enough for the OP's age. When I was 13, I think the only physical activity I really did was basketball.
For exercise, i'd recommend if you have a smart phone, get an app like runkeeper or something and track all your work outs. It's pretty good cause you can get audio queues and training plans etc to help you build up endurance.
For weight control, just stop eating crap. Watch your calories in. Cut out soda's, sugary crap etc. Do this for 6 days of the week and reward yourself with something nice on the 7th day. Don't go overboard though, just something nice you've been craving.
Theres a doco called Fat, Sick and Nearly Dead. give it a watch.
My weekly podcast can be downloaded here this week what happens to imaginary friends when you murder them??
Go for a run, all you need, or play a sport
My favourite exercise is lifting weights.
For cardio, I lift heavier weights.
Chins 15-20 total reps, add weight or use assisted.
Rows 3x5 SUPER STRICT.
Optional: Cable rows, 3x8 bicep work, 3x8 rear delt flyes, do this at your own discretion. If you don't feel like it, don't worry
Front squat 3x5
MP (military press) 3x5
Optional: 15-20 reps of dips, 3x8 tricep work"
Those are the two workout days I'm currently doing. I would recommend looking up how to do these exercises before performing them.
It's recommended you workout more than 3 times a week, however be sure to take rest days as lifting heavy ass weights is pretty tiring . Day B in particular is very exhausting, heavy compound movements like the deadlift and the squat can really take a lot out of you.
Source of program
Running is the best, (30 minutes to 1 hour)
Go play soccer or basketball, It will get you in great shape.
So would this work?
Cardio Activities 45 mins on one of the days
Weights 45 mins one of the days
All around body activities 45 mins one of the days
and if i was to do the weights, i am just naturally well muscularly built, would 5 KG be a good starting point?
And when do you regenerate your body?