Like this, I ever installed an application and somehow I didn't know how to uninstall it so I just deleted all of its files from program files folder, included its uninstall file. Little did I know that the cache of it still appear in the settings.
When I wanted to uninstall it Windows told me that Windows cannot find uninstall.exe. After looking for the solution online, I did a very unconventional way to delete it, I deleted the program key from Windows Registry. After that, I can delete the cache of that application.
I'm actually scared of what I've done but I'm pretty sure that I only deleted one folder from the registry, the folder titled the name of the application developer. It is one of the most important parts of Microsoft Windows operating system. Hopefully there won't be any problems with my sister's laptop.