Can iphone 5 LTE data plans be changed? (AT&T)?

Like if i i had 3 gb a month data plan, can i change to 5gb?

this is for AT&T

Changed up yes. Down, I don't think so.
Two things.
1. Check your bill to see exactly what the monthly average is you're using. If it's close or under, why chalk up extra cash like that? That's what Wi-Fi is for--to make that cell data stretch the month and use it when you don't have Wi-Fi.
2. If you just want to gobble data--er uh download movies and such, you better think twice. If you are data hogging, they can and WILL throttle you and that 5gb will creep in at < LTE speed after probably 2 or so. Or worse, cut you off for certain time frame--like days--or kick you off for good.
Best luck.