How to change motherboard logo

Motherboard logo is fixed in the BIOS. Without embedding a new graphic in a copy of the BIOS and then flashing it (very risky), all you can do is turn it off.

Now, the boot logo is another matter. That can be changed pretty easily. Google something like "change boot logo".
 
There are boards that will allow you to change the motherboard logo or splash screen during POST.
I remember reading somewhere in my motherboard manual there is a way to do exactly that. Read you manual and find out if your board will let you do it. If not, as mentioned, all you can do is turn it off.
 

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