V9.04 Start-up problem

[Peter Baily]

I upgraded to 9.04 from a fully up-to-date version of 8.10 by 
download.   On start-up the message appears: "Failed to open file 
'/usr/share/gdm/themes/Human Circle/Human/ubuntu.png': No such file or 
directory".   The boot file seems to be attempting to call the start-up 
screen from 8.10 which clearly has been deleted.   Please can anyone 
advise a relative novice as to how to delete this call from the boot 
file safely?

Thanks!