You can upgrade your monthly plan at any time in the Subscription section.
For example, I'm on a Growth monthly plan and want to upgrade to a Pro monthly plan.
Since I have used 2007 of the 5000 requests available, the remaining 2993 requests will be rolled over on top of the new monthly usage:
The extra pack will be always visible when clicking on the profile image in the top right corner of the page:
N.B. When upgrading your plan the new subscription will be applied immediately and you will have access to the new number of requests associated with the new plan. A new monthly plan will also start from the upgrade date.
The only reason this would not be the case is if your account gets frozen upon purchase, in which case you should get an email from us with the necessary steps to fix this.