If I upgrade in the middle of a billing cycle, do I need to pay the full amount for the new subscription?

NO, you don't need to pay the full amount for the new subscription if you upgrade in the middle of a billing cycle.

Instead, the subscription fee is calculated based on the price difference between your current plan and the new plan, considering the remaining period of your billing cycle. This ensures you only pay for the upgraded plan from the time of the upgrade onward.