If your phone’s network reads “Sprint” or “AT&T” in your phone’s settings or in the top left corner of your phone, then the below article applies to you.

Upgrading mid-cycle: You can only upgrade your plan for the upcoming cycle. The plan upgrade will not take effect until the next cycle begins, which is when payment for your new plan will be made. 

If you'd like to add data immediately because you've used your allotted amount you can also do so through the Wing App or Wing Dashboard. You will simply pay the difference between your current plan and the higher GB plan you choose. It will go into effect immediately.

How to check your network :
iPhone : Settings —> General —> Network
Android : Setting —> About Phone —> Network
Or : The network name in the top left corner reads “Sprint” or “AT&T”.