It's going to sound painfully simple, but you just need to start eating whole foods. The best way to limit one's sodium intake is to simply avoid packaged food as much as possible. I used to eat terribly, and it was definitely a learning process to figure out how not to do that.
Wander around your local grocery or health food store for a while (on a full stomach) and look at what they have. Start adding veggies and fruits in your diet. Avoid frozen meals and soups as much as possible (frozen meals have a TON of sodium). And get yourself a cookbook from the bargain section of your local bookstore. The easiest go-to for me is salad and smoothies. They keep me full, give me nutrients, and make it easier for me to stand the ten or so minutes it takes to make a meal (when I get hungry, I do not feel well at all). If you can, ask whoever lives with you to limit the unhealthy snacks they bring into the house.
It seems overwhelming at first, especially since none of us was really taught what to eat, but you can do it. You just have to commit. Remind yourself of why you're doing it.