Here is a step-by step guide with images to know how to dual boot Windows 7 or 8 with Windows 10 OS:
Step 1: Creating another partition for Windows 10 in your system
In order to install Windows 10 to another partition on your Windows 7 or 8 operating system, you will need to create a new partition for Windows 10 in your hard drive.
(Note: If there are two different hard drives in your computer system and you are using only one hard drive, then you can skip the step of creating another partition for Windows 10).
You can resize your Windows 7 or 8 partition to create a space for Windows 10 using the ‘Disk Management Utility’. For this, press Windows key + r which will open up ‘run command’. Then type ‘diskmgmt.msc’ into the run dialogue box and press enter to launch the disk management utility.
The Disk Management Utility will be open up like this: