Detailed steps to help me lose weight?

If it matters, im 16 about to turn 17. Im wanting to lose 40lbs. Currently I weigh about 172lbs and im 5'1. For the past month iv been walking a regular 3 miles some days 4miles. I set small goals for myself so I cab reach my goal weight. Ex. I want to lose 14lbs in the next 15 weeks. But I need some tips and/or steps on what I need to do, I dont really much of a guide on what I should and shouldn't do. (Btw IF you just wondering for some reason, Im just wanting to do this to get in shape and as well as my health of course, also im not wanting to be stick skinny or anything :])