Question

Difference between upgrade and custom installation

Answer 1

A Clean install is usually defined as formatting the driver (either by the user or by using Setup) and then installing the OS. A custom install is defined by Microsoft as installing the OS on the same partition as a previous installation of Windows. Note that this is not the same as an upgrade.
because it looks like that you installed a new version of windows
bt actually upgrade means you don't loose your apps settings pics movies etc