If you'd like to change the Big Value Bundle you're using, first make sure you have enough credit in your account to get the one you want. Then, just text one of these codes to 49501:
Once you've changed to a new Big Value Bundle, you'll be charged the new amount every 30 days unless you change again or remove your bundle.
If you buy a new Big Value Bundle before your existing bundle ends, your current allowances will be replaced with your new bundle allowances. Any remaining data, minutes and texts won't be rolled over.