This theme is ideal for computers which don’t have compatible hardware for video graphics acceleration and can do without eye-candy features like transparency. Here’s how you can get back the Aero Lite theme in Windows 10.
1- Download Aero Lite Theme from here.
2- Navigate to C:\Windows\Resources\Themes.
3- copy WindowsBleuaerolite.theme file from desktop to C:\Windows\Resources\Themes
4- Now right-click on desktop -> Personalize and there you will have “Aero Lite” theme installed and ready to use as you can see in the first picture.
Method 2 "manually"
1- Navigate to C:\Windows\Resources\Themes and Copy the default aero.theme file to your desktop.
2- Now right-click and open the copied aero.theme file with Notepad/Notepad++ or the text editor of your choice.
Inside the opened aero.theme file, you will find a property named DisplayName under [Theme] section. Replace the string after equal sign (=) to any name of your choice. Let’s call it Windowsbleu.com Aero Lite
3-You will find another property named Path under [VisualStyles] section (at the end of file). Change Aero.msstyles to "WindowsBleuAerolite.msstyles" as exemple, so that it points to the new theme we just created.
That’s it. Now save the file. Also for the sake of simplicity, rename the file that you just edited from aero.theme to WindowsBleuaerolite.theme.
The final step is to copy WindowsBleuaerolite.theme file from desktop back to C:\Windows\Resources\Themes
Now right-click on desktop -> Personalize and there you will have “Aero Lite” theme installed and ready to use as you can see in the first picture.