1. Open Control Panel
Click on start and then type in Control Panel and press enter.
2. Double click on System
Double click on the System Icon.
3. Navigate to change settings
Under Computer name, workgroup and domain settings click on Change Settings.
4. Change settings to join domain
On the Computer Name tab, click on Change and then select domain and enter in the domain name and press enter. Once prompted, enter in the username and password of an account that has permission to join a domain and press enter to join the domain. Restart when prompted.