We have posted a detailed tutorial in past which shows you how to remove Branding logo from Windows 7 login screen:
If you want to customize the branding logo i.e. change the branding logo text, following utility will help you:
"Windows 7 Branding Changer" is an excellent, small and portable utility created by "myjuman" @ DA which allows you to change Windows 7 login screen's branding logo quickly and easily.
You just need to create a PNG file using an image editing software like Adobe Photoshop, Gimp, Paint.NET, etc, then select this PNG file using Load Picture button and at last Apply the image. It'll immediately change the text.
For your information, it modifies "Basebrd.dll" file present in "%windir%/branding/basebrd" folder and replaces the existing image with your desired one.
You can create the PNG image of 350x50 pixels.
It works perfect in 32 and 64-bit versions of Windows 7.
You can download it using following link:
Download Link (removed by developer...)
You can also check out following similar tools to customize Windows 7 login screen: