There are couple of options to install Windows 10 on your PC.
1. Install directly on your PC, but take your backup as downgrade is not supported.
2. Install VMware workstation 10 on your exiting PC & install Windows 10.
3. Install Virtual Box on your PC & Install Windows 10.
In this post we are going to install Windows 10 on Virtual Box , so lets start.
To install Windows 10 Tech Preview, first you need to sign up for the Tech Preview program and download the ISO from http://preview.windows.com.
Download and Install Latest version of Oracle VirtualBox.
So lets start,
To set up Windows 10 in VirtualBox, launch the VirtualBox and click New in the VirtualBox Manager window to create new Virtual Machine. Enter "Windows 10" as the name of the operating system. Select the Windows 8.1 64-bit as the version and click next.