Installing Windows 10 to the partition you created: Verify your BIOS is configured so that the DVD drive is the first boot device (or USB if installing Windows 10 from a bootable USB flash drive).
Disconnect all non-essential internal disk drives and external drives and accessories.
While Windows Vista is running, insert the Windows 10 DVD / USB flash drive and Restart / reboot the computer.
Press the keyboard’s space bar several times when you see the message displayed below.
Wait for the Windows splash screen to be replaced by the Windows 10 Language, Time and currency and Keyboard setup screen. Make any changes (if needed) and click the ‘Next’ button.
Click on the “Install now” option located in the center of the screen.
You will see “Setup is starting” message.
Read and accept the License terms and click ‘Next’.
Which type of installation do you want? Choose the “Custom: install Windows only (Advanced)” option.
1) Where do you want to install Windows?
Select / highlight the partition that you named “Windows 10” if you pre-formatted the partition and entered a Volume name or select the “Unallocated” space you created after shrinking the Windows Vista partition.
Click ‘Next’ to continue. 2) Windows 10 will now start a series of installation steps, followed by a restart / reboot of your PC.
You can click here to see a series of screen shots of the automated part of the Windows 10 Technical Preview. No user input or action is required on your part or you can click here and skip to the point in the installation process where you are required to provide input.