Hello minichien
You just need to download this tool if you dont have it:
After you downloaded it, you have to open the data.sah in your client with this tool.
Then a screen opens (the data of your client). There you go to the "interface" folder where you have to scroll down to the file "sonovlogo.bmp". Right-click it, click "Import" and find your edited "sonovlogo.bmp" (it needs to have exactely the same name or it won't work).
Thats all
If it asks you to create a patch, just klick "No" its not necessary.
I hope i could help you. If you still have questions or problems, don't hesitate to ask.
(If you want, you can add me on skype)