If there are two windows in the computer, then do it as a dual boot  manage.

Dual boot or multiboot means that if you have installed two or more operating systems in your computer, then Dual Boot can work in any of these two operating systems. Let's know how to manage it - 

Suppose you have Windows 7 installed on your computer and you found out that the preview of Windows 10 is also locked, then test it as well, that is, you installed both operating systems on your computer, but  after Windows 7 After installing Windows 10, Windows 10 becomes your default operating system, i.e. Windows 10 is open when you turn on the computer. Can be bothered, one way is to keep your old system default - 

1. Click on Start button and open Control Panel. 
2. Click on this system, or press the Windows logo key + Pause button, this will open the System Properties of your computer. 
3. Click on Advanced System Settings. 
4. Now click on the Advanced tab and under the Startup and Recovery you will see the settings button. 
5. Here you will see a list of all your operating systems. Now select the operating system from the list that you want to select as the default operating system, i.e. if you restart the system, then your old windows will be open. 
6. Along with this, you can also change the time of the dual boot screen, like 30 seconds or less as you want.