Simply download the free application, run it and click Change Logon Screen. The application will prompt for the location of the new background image and then install the new screen behind the scenes. Tweaks.com Logon Changer will even provide a preview of your new background on a logon screen.
When you have settled on a good logon background, click the Test button to see it in action.
Users don't need to worry about the 245KB limit imposed by Microsoft. The Tweaks.com Logon Changer will give you the option to automatically resize and recompress the image to the highest quality possible. The original image is left untouched.
If you want the default Windows 7 logon screen back just click Revert to Default Logon Screen and the application will automatically uninstall any customized screens.