Hey gents, recently I decided I wanted to change my grades around, and do something with my life
First, start with an honest assessment of where you are now, and how to improve your chances. In my experience, one doesn't just wake up one day and improve their grades. What are you going to do different to get better grades. Keep in mind, "decent" grades isn't going to cut it.... you need to get great grades, strong ACT/SAT's, and then be prepared to present a compelling case to Admissions that you know you had a slow start but turned it around , set a goal and accomplished it.
It's not just grades and SAT's -- you need a strong record of leadership, activities and athletics to be competitive. Find something you are interested in, and strive for excellence,
Finally, why do you want to attend USNA --if your goal is to serve as a Navy /Marine Corps officer, there are other paths to a commission, and I would suspect that with some, like OCS, your high school record is of little relevance. If you turn your academic performance around, attend college and apply to OCS, you will end up in the same place (0-1) as if you are a USNA graduate.
You are starting behind the power curve , while many USNA candidates have been preparing themselves for years. That being said, if you don't try, your chances are zero. It's great that you have identified your goal, now is the time to come up with a plan for achieving the goal and then executing it.