In Windows 7 and Windows 8.1 users you can turn on or turn off a guest user account using the User Account section available as part of Windows Control Panel. Windows 7 users can access Control Panel via Start button.
Accessing Control Panel on Windows 8.1
Windows 8.1 users can access the control panel by right clicking on Windows logo and selecting Control Panel from the list.
Another alternate way to access the Control Panel is through Charms bar. Click Settings on Charms bar.
Then click Control Panel available at the bottom of the PC Settings.
Enable or disable guest account on Windows 7 and Windows 8.1
And to manage user accounts you can click on Control Panel -> Add or Remove User Accounts (User Accounts and Family Safety). This would display the following Manage Accounts window
On selecting any user you can either turn on the user if it is disabled or you can turn off if it is enabled. For instance in the picture shown above on clicking Guest the following Turn on Guest Account window would be displayed if the Guest account is disabled.
And to turn off a user account, click on the Turn off the “User” available on the left hand side.