Sure. Open the first menu, hold down the right-mouse button over the image of the cat and select Global Settings. Go to Images&Icons settings and change the Logo Image.
Note that your changes are saved immediately. This is because Auto-Save Preferences option is enabled by default. Before you start experimenting with AmiStart prefs I would recommend to disable this option. You can always save the preferences manually.
For more information check the AmiStart's documentation in AmiKit:Utilities/EXPANSION/AmiStart folder.