Just go to google and search for Virtua Tennis 4 icon and you'll find a lot of possible icons.

1. The file already is a Icon (.ico)
- Save the file on your computer
- Right click on the game shortcut.
- Choose "properties"
- Choose the tab "Web Document" if it's not already chosen
- Click "change icon"
- Search for your file
- Choose it, press ok, press ok on the properties dialog
- Finished

2. The file is a PNG (.png)
- Save the file on your computer
- Go to http://convertico.com/
- Convert the file and save the converted file on your computer
- Proceed with this file as shown above (1.)

I use the file found here[www.deviantart.com]. The original downloadpage is deviantart[kingacid.deviantart.com].