Fit into my skinny jeans?!!?

Im about 5'3" and 195LBS ( i KNOW I NEED to loose weight) Im going to loose the weight in 6 months, I am only 16 so I think If I work out and go on a diet I can do it. I want to be in a size 7 again in women's jeans... how much to do you think I should weight to fit into them? and also what is a good fast working diet... I hate atkins but it does work fast and its not too too hard...