I am 12 140lbs how do I loose wieght am I over wieght? Am I obese?

It is more about your built and your height then your age, so I can not say if you are obese or not for sure. However unless you are really short like 3' tall ( lol ) I doubt you are.

However if you think you need to lose weight and have your parents permission, I suggest you do two things. 1. drink more water 2. exercise. If you do these two things and eat healthy ( even some what ) you can nip a weight problem before it is a "big" problem. I admire young people who want to get a handle on their weight/health now, yet be careful not to go the other way either and end up too skinny and/or with a eating disorder.

If you are tall, then 140lb could well be your correct weight.

If you are a bit overweight, then cut out the junk food, especially sodas and anything sugary or deep-fried. Get more exercise (can you cycle to school?), drink water, eat more fruit and vegetables, and go to bed on time.

Do not worry too much about it, 12 is a very awkward age, you may well grow into your weight.

Stay away from the junk food and get moving. Dance exercise walk everyday...
But you are still developing. You may still be carrying baby fat, as you get taller your weight may even out.
But do watch what you eat and exercise. It is a good time to develop good eating habits.