Here are the steps to Uninstall windows 8 from a dual boot without a software.1. Press the Windows key plus R in your keyboard.
2. In the Run window type msconfig and click OK
3. Select the Boot tab.
4. Select Windows 7 and click on Set as default.
5. Then select Windows 8 Developer Preview and click Delete.
To reclaim your Partition:
1. Right click Computer –>> Manage –>> Disk Management
2. Select the partition where you installed Windows 8, Right click Delete volume, yes to the warning.
3. Right click Drive C: to extend volume make sure the partition is selected, click on next then finish the wizard.
That is it. Let me know how it went?