menu next to the project's name) and click the red Leave project button in the Leave project section; Leave project in the ... menu of the project's row in Projects does the same. SyncNow asks you to confirm first.
Your membership ends, the project disappears from your SyncNow and you can no longer use its hosting and database connections, which stay with the project for the owner and the other managers. The owner keeps the project, its website is not touched, and neither are your local files.
Only the owner can give you access again, by sending a new invitation. The owner cannot leave a project: they remove it instead, which closes access for every manager. Leaving is not removing: when you leave, the project stays for the owner and the other managers.