Windows 8 won't allow you to connect your computer to more than one domain at a time, nor will it allow you to connect your computer to a domain and a workgroup simultaneously. If your computer is joined to a domain already, but you want to connect to a different domain or to a workgroup, you must leave the domain to which your PC is assigned. Alternatively, if you're a business owner or administrator and you want to disjoin a computer from your institution's domain, you can do so through Active Directory Users and Computers.
Via the Control Panel
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Step 1
Sign in to your computer as an administrator. Press "Windows-W" to open the Settings screen and then type "sys" into the search box.
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Step 2
Select "System" from the results to open the System window in the Control Panel and then scroll down to the Computer Name, Domain and Workgroup Settings section.
Step 3
Click "Change Settings" to open the System Properties window and then click "Change" to view your domain membership.
Step 4
Select "Workgroup" from under "Member of" and then enter a name for the workgroup, or use the default name. Click "OK" to leave the domain.
Via Active Directory Users and Computers
Step 1
Log on to your domain controller as an administrator and then right-click an empty area on the Start screen.
Step 2
Select "All Apps" from the context menu and then choose "Active Directory Users and Computers" from Administrative Tools.
Step 3
Select "Computers" from the console tree and then right-click the appropriate computer in the details pane.
Step 4
Choose "Delete" from the context menu to remove the computer from the domain.