Hey Nicolas, thanks for the message and great inquiry!
We don’t prorate costs or credits for plan upgrades (except for one-off credit packages). Upgrading gives you the full set of credits for the new plan. For example, moving from Starter to Explorer provides all Explorer credits. Our team is reviewing this and may implement changes in future updates.
If you’ve upgraded or are looking to, we can refund the lower plan so you can buy the higher plan, this will adjust the corresponding credits. Let us know if you'd like to proceed!