Welcome!
I will say the same thing preview posters have said.......start small and go from there. For example, start by cutting out soda completely or if you can't give up soda, switch to diet.
When I was 18 ( I am 25 now) I went from drinking 8 cans of regular coke a day, to diet. In 2 months, I lost 25 lbs.
You can do it.
And never say something is too hard to achieve. It is all about how you have your mentality set. If you think you are too tired to workout, your body will feel tired and you will eventually plop yourself on the couch and wait until tomorrow to exercise. This is where you need to hot-wire your mental state to where YOU KNOW you can do anything you set your mind to.
Good luck!