You can change your subscription level at any time in the App Settings -> Subscription -> Change plan
When upgrading/downgrading your subscription plan, your new subscription starts immediately. All remaining days of your current subscription are converted into days on the new plan. You're going to be charged upon expiration of these days.
If the subscription level is downgraded or its billing period is changed, the plan will be changed and the funds will be charged after the end of the current subscription period.
When you upgrade your subscription, the new plan will be applied immediately, and any leftover days will be refunded back to you in a few days.
Please note, a subscription can be changed on the platform where it was purchased. In case it is more convenient for you to subscribe from another platform, you need to cancel the current subscription or its auto-renewal, wait for for the subscription to expire and then subscribe again from the corresponding platform.