If you upgrade in the middle of your subscription period for your current paid plan, then you will be charged for the price difference between the current plan and new plan. On the next recurring you will be charged as per your new plan.
1. To Upgrade, Click the Menu icon.
2. Now click Settings.
3. Compare all the plans and click on ‘Upgrade Plan Now’. After that, Add Payment Info to start using the upgraded plan.
While in case if you downgrade in the middle of your subscription period for your current paid plan, then amount will not be credited at a time. But the next recurring will be according to your new plan.