Hey,

You could try to use something like HackBGRT if you have a UEFI bios. That program can be used to change the Boot logo.
Alternatively, if you have an older BIOS, check the EFI partition, the file named "bootres.dll" on there can be opened with Resource Hacker and should contain the logo.

Be warned, though, changing the boot logo has a high risk of breaking your installation.