Microsoft’s latest operating system, Windows 10 is available for download since a few days ago. However, this possibility Technical Preview version still contains many bugs. So, you should not remove your old operating system when using Windows 10.
There are several alternatives to do so, one of them with a dual-boot. Although this method is quite safe, it is advisable to perform a data backup first. Here are the steps as we quoted from howtogeek
Install Windows 10 Technical Preview
First of all, you have to set up a space on the hard disk to install Windows 10 first. If you have more than one hard disk, you can directly install Windows 10 on your hard drive. But if not, you have to partition the hard disk to “insulate” the old operating system and a new operating system.
To make a partition, you can use the Disk Management Utility which is provided by Windows. To access it, press the Windows key + R, and type diskmgmt. msc in the Run dialog box, and press Enter.
On partition C: \, right click and select “Shrink Volume.”
Microsoft says that Windows 10 has the same system requirements as Windows 8 64-bit version of Windows 8.1 itself requires at least 20 GB of free space.
Once space is available for Windows 10, you can now install Windows 10.
Windows 10 installer file iso format you can load DVD or to USB Flash Disk. To enter it, you can use the software Windows 7 USB / DVD Download Tool.
After the installer Windows 10 already available on DVD or USB Flash Disk, restart the PC / notebook, and then point the flash disk or a DVD on the boot menu.
Navigate to the installation of Windows 10 partition that has been prepared in advance.
After the installation process is complete, you can choose one of the operating system installed on a notebook / PC.