Windows 10 login screen background

Hello today I just upgraded from 8.1 to windows 10, everything went fine but I'm stuck on a simple thing.

How on earth can I change this really bad blue background on the windows login screen right after the lock screen?

I've tried changing images in C:\Windows\Web\ directories but nothing changed.

That background is driving me nuts...

UPDATE

So far the only thing that helps me get ird of the image is this (I'm posting the contents of a .reg file):

Windows Registry Editor Version 5.00

; Created by: Shawn Brink ; http://www.tenforums.com ; Tutorial: http://www.tenforums.com/tutorials/9108-sign-screen-background-image-enable-disable-windows-10-a.html


[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\System] "DisableLogonBackgroundImage"=dword:00000001

First, click start and then select settings from the settings panel.

When the settings app opens, select personalisation and then lock screen. from here, you should be able to select a lock screen wallpaper to use.

If its the password entry screen you are looking to change, things are somewhat more involved, so take a look at This app which can accomplish this for you quickly and easily.. worked for me.