Hey @LolghElmo - thank you for joining us on the forum!
First, I want to start by distinguishing the difference accounts vs. teams in Figma.
When it comes to plan subscriptions and seat types, those are determined on the team level, and not the account level. This is because your account can be part of multiple teams for multiple reasons.
When you say you want to change your seat from full → dev, your intention is to do this in a team you own and are an admin of, correct?
A couple of resources I want to provide you:
How seat changes work in Figma: https://help.figma.com/hc/en-us/articles/360039960434-Manage-seats-in-Figma#how-seat-changes-work
Instructions on how to downgrade a seat: https://help.figma.com/hc/en-us/articles/360039960434-Manage-seats-in-Figma#change-seat-type
This should give you a good starting point on how to downgrade on your end.
Per our terms of service, subscriptions are non-refundable. Please visit this page for additional information.
Thank you!