This is better done before you open Creo. Save the default Creo start shortcut to a new name. In the new shortcut, change the "start in" folder. In the Start-in folder, create a file called config.pro. the only thing to add into the file is:
graphics win32_gdi
Now use the new shortcut to start Creo. This will read the new config.pro file from the start folder. once Creo is open, you can confirm the settings is in effect by looking in File>Options.