To get more data on your phone you can simply switch plans to one that has more data. If you have a tab plus you will need to select from the current selection of tab plus plans but if not, you can select from any available plan
What plan do you have? If you have an older plan, it might be cheaper you just pay overage charge. (My son is paying $0.02/mb for his data overage) Check your data overage rate and compare with current plans they're offering.