How to uninstall or remove Windows 10 from a Windows 8.1 dual boot computer January 6th, 2015
Since we will be removing Windows 10 and keeping Windows 8.x, the first thing you will need to do is boot to 8 or 8.1 and following the steps listed below.
1) If you have not created any Image Backups while you were evaluating Windows 10: The first thing you need to do is to install an Image Backup software package and create a backup of the entire disk drive (all partitions) to an external USB drive. This is your safety net should something go wrong and you cannot boot to either version of Windows, just restore the image you created.
After the backup has been created eject the USB drive and disconnect it.
2) Run Msconfig: In the ‘Desktop’ mode, right click on ‘Start’ and in the pop-up list, select the ‘Run’ option.
Type: msconfig and tap the ‘Enter’ key.
In the Tiles or ‘Start’ screen mode, in the upper left corner click on the ‘Search’ icon.
In the ‘Search’ box enter: msconfig.exe and tap on the msconfig.exe entry at the top of the list.
3) Click on the ‘Boot’ tab to display the versions of Windows that are installed. Windows 10 should be the 1st entry in the list (show as the ‘Default OS’) followed by Windows 8.1 (or 8).
4) Select (Highlight) the Windows 10 entry and then click / tap on the ‘Delete’ button.
Now set the ‘Timeout’ value to 3 seconds and click the ‘Apply’ button.
5) Click on the ‘OK’ button to exit msconfig’s ‘System Configuration’ window and when prompted restart the computer.
6) Run the Disk Management utility (Right click on the Start button and select ‘Disk Management’).
At this point you can choose to keep the partition for installing future builds of Windows 10 by simply formatting the partition to remove all the Windows 10 operating system files (Step #7) or use the space to increase the size of the Windows 8.1 partition (Steps #8, 9 and 10).
7) To format the partition, right click on the Windows 10 partition and select the ‘Format’ option. Users with a Hard Disk Drive (HDD) should use the ‘Full’ format option. Solid State Drive users should use the ‘Quick’ format option.
8) To delete the partition, right click on the Windows 10 partition and select the ‘Delete Volume’ option.
Click ‘Yes’ when prompted to delete the Windows 10 partition.
9) To add the now ‘Unallocated’ space back into the Windows 81 partition: Right click on the Windows 81 partition (C:) and select the ‘Extend Volume’ option and follow the Extend Volume Wizard’s guided steps.
10) Now follow the Extend Volume Wizard’s guided steps.
Verify the disk with Windows 8.1 (or 8.0) installed on it (Disk 0 in this example) is selected if you have more than one disk drive. The 200GB of unallocated space (204799 MB in binary notation) should be listed in the ‘Selected’ box. Click on the ‘Next’ button.
Now click ‘Finish’ when prompted.
11) Your Windows 8 or 8.1 partition should now show an extra 200GB has been added to its size. As shown in the screen shot the partition size is now a total of 465GB. Exit Disk Management.
12) Now create a new Image Backup of the entire disk drive.