change login window ,splash screen

Hello everyone,
I’m very much new to linux using 11.3 Gnome. I want to change my login window and splash screen. I went through lot of sites but I couldn’t find the answer. Please guide me through the process.
Thank you

This thread was moved fron General Chitcat (where it explicitly says: PLEASE do not post help questions here) to Applications.

To the OP: I hope you will get some reactions on your thread now it is in a place where the Application people are looking. Next time post in the correct forums yourself please, we volunteers are not here to look around the whole day for misplaced threads and then move them.