Renewing plan before autopay due date

You have a couple of options, one of them is to use the option of a data add-on. If you log into your account go down to add-ons you will see the option to add a limited amount of data.

The other option is to renew your plan early. The only way to do that is to go through the change plan option, and select a new plan, or even your same plan and confirm that you want to change your plan. This will require for you to pay for the plan and it should begin immediately. This means you are on a new 30-day cycle that will be different from the cycle you have been using.