What is the best way for me to get into shape?

I'm 16 years old, female and am about 160 lbs. My goal weight is around 130-135, I'd like to do this by the middle of august. I want to not only be skinnier, but also get in better physical condition. I want to get in shape so i can do two activities: Parkour and Martial Arts(I was a black belt in Tae Kwon Do by age 11, but haven't gone at all since i was 13). Another goal is for me to get more limber, flexible and have better balance. I currently lift weights 4 days a week for about 30 minutes in a weightlifting cl at school. Im not really eating healthy, I do have the occasional bag of chips, candy bar and/or ice cream. I also love soda. What should i do to get in better physical condition?