In order to upgrade your PiPiADS subscription, you have to simply click on the current membership plan. There you will see an "upgrade" icon that you can click on. It will display the other membership plan, which you can click and upgrade as you desire. If you decide to upgrade your subscription before the expiration of the current plan, rest assured that you will not lose out on time left in the previous plan. The remaining days or months left will be added to the duration of the new plan.