1. EasyBCD is a free utility which can be used to uninstall Windows 8 Developer Preview. For this, you first need to download and install EasyBCD application on Windows 7.
2. After installing EasyBCD, run it. Click on Yes if prompted by User Access Control
3. Now, click on the Edit Boot Menu button. You will see the entry named Windows Developer Preview. Select it and click on the Delete button.
4. A confirmation prompt will pop up. Click on Yes.
5. Now, you have just removed the Windows 8 Developer Preview entry from your boot menu. Click on Save settings and close the application.
6. The last step is to format the partition where you had installed Windows 8 Developer Preview to get your disk space back.
Following these steps, you will have successfully uninstalled Windows 8 Developer Preview from your computer completely.