Right click on the My computer icon. Go to Properties
Then System Properties dialog box will appear.
Click on the “Computer Name” tab In the System Properties dialog box.
Click on the “Change” button to rename the computer.
Then “Computer Name Changes” dialog box will appear.
Click “OK” button after you type the computer name.
You must restart the computer for changes to take effect.
Also you can change the workgroup name by using these steps.