@endomain It's a little different for each laptop. Here's a good tutorial: https://ittutorials.net/computer-repair/laptop/change-bios-boot-screen-logo-image-lenovo-laptops/
Your bios update program will probably have a file like "Logo.txt" that describes the details for your laptop. For example, for mine, I had to name the file logo1.whatever, and only the Gif version of the image worked right
A bunch of technomancers in the fediverse. Keep it fairly clean please. This arcology is for all who wash up upon it's digital shore.