I've just gone off from a supporter to a normal player and I took a res on utopia do I keep the res or do I have to give it up?
You keep any claimed residences, but if you unclaim it, you can't claim it again until you're supporter again.
This might be a good read: https://empireminecraft.com/threads/guide-so-what-happens-if-your-voucher-expires.48926/