Using hosted service, how do I release an instance name that I don't need to use anymore, or reuse an older one

I created an instance name, and update to a different one later. But when I tried to change it back to the original, it doesn’t not allow me to, getting " Your instance name is invalid. It is already used by another instance. Please try a different name."
How can I reuse the old one, or better yet release that name so someone else can use it?

Hi @mangqin
Contact support with the details you’re trying to do.