A User can disable Guest Access in one of two ways.

From the Users Page under Account Settings, an Admin can select the ellipse on the right-hand side of the Guest they wish to disable.

The User can toggle "Enable account access" off from this screen to disable access.

From the Website Dashboard, the User can select the "Share" button on the top right.

The User can select the red "X" to revoke access.

Once the Guest's Access is disabled, it should reflect as "Inactive" on the Users Page.