Help a brother out!

I recently bought Battlefield 4 for my PS3. What an awesome game! My issue is after unlocking battle packs for two weeks and getting upgrades, I haven't figured out how to actually change to them. Example: I earned an RPG, but can't find out where in the game to choose to use it! I'm still using my original bolt action sniper rifle even though I have the next upgraded one. It's very frustrating!