sorry to be a bit dumb but how do u upgrade weapons in this game?

If your talking about attachments then you have to complete the challenge missions.

Its pretty easy to figure out with some exploring-go to the section that talks about customization or something named like that, go to weapons, and customize each of them individually.

they're both right...you unlock "attatchments" by doing challenges and then equip them in he flashing tabs labeld weapons you don have to customize them all just the ones you use

Ive done all the challenges but for some reason and wont let me unlock the second star weapon and items in be more objective, escort duty, and tower defense on xbox 360 can someone help me with that