Re: how to modify weapons on battlefield 4
There are two ways to change your loadout, in-game or via Battlelog. If you are in-game at the deploy screen, click Customize in the lower left corner of your screen. This will open the loadout page where you can change your weapons, attachments or gadgets for your soldier or your vehicles (you can switch between the soldier and vehicles by clicking the tab on top of the loadout list).
Once you've played a round in-game you will also be able to change your loadout in Battlelog directly. To do so, click Loadout in the soldier menu by moving the mouse over the soldier tab in the main menu. Once you've updated your loadout in Battlelog, don't forget to hit the save button in the top right corner 🙂
Hope that helps, let us know if there are any questions.