Roles and permissions
The four roles, what each one can do, and which decisions are owners only.
Everybody in an organization has exactly one role. Roles are set when you invite somebody and can be changed later by an owner or an admin.
There is always an owner
An organization must keep at least one owner. If you are the only one, you cannot leave, change your own role to something lower, or be removed, until somebody else is made an owner. The refusal says so when it happens.
This is not a technicality. An organization with nobody in charge cannot invite anybody, cannot change billing and cannot be recovered without us intervening in the database.
Changing somebody's role
On your team page, pick the new role next to their name. It takes effect on their next request, because roles are read from the database on every call rather than baked into a token that would keep working until it expired.