Keep on playing, buy packs with credits from Daily Tournaments, sell cards. Don't keep any of your starter deck. If you need some of them later (some budget Sentinels use Carlos because Melvin is expensive), then you can always buy them again because they are super cheap. (Or will be to you by the time you get to that point).
If you REALLY want to keep La Junta / Sentinel, then I'd save up for this deck for now:
Burger will get a little on the expensive side but he's worth it. Note that this isn't a very good deck, but as you get more clintz then you can save up for the better cards like Bryan, Hawk, Lehane, and eventually, Melvin.
I wouldn't recommend Sentinel / La Junta for beginners though, I'd recommend something more like this:
Again, Fabio and Rosa can get on the expensive side for beginners but it's not hard to save up for them.