Launch Boot Camp Assistant from the Applications:Utilities folder.
Click the Continue button.
Check only the Install or remove Windows 7 option and click Continue.
Choose Restore disk to a single Mac OS partition and click Continue.
Click the Restore button to begin.
You will be asked to login with your Administrative username and password. Enter these and click the OK button.
You disk will now be repartitioned to remove the Windows volume.
You will be informed that your disk has been restored as a single volume. Click the Quit button.