Q: How do I convert a user into a guest?
A: To do this, remove the user you've selected, and then add them back by using the 'Add contact' option.
Additional Q&A
Q: How can a user who has transitioned into a guest view their proofs?
A: They can view their proofs either through the public URL or by clicking on a link sent to them in an email notification.
Q: What occurs with the proofs of someone who's been removed as a user and later added as a guest?
A: If the person hasn't been removed from the proofs entirely, they will still have the role of a reviewer. If the guest has access to emails containing personal URLs, they can still view the proofs shared with them. Deleting contacts from the People tab doesn't automatically remove them from the proofs they're reviewing. To do that, you'd need to use the option to remove them from all proofs, and this applies to both registered users and guest contacts.