I have the TR but I think the buttons are similar (if not the same).
1. When you 1st power up your board, the "combi" button on the top left side of the screen should be lit.
2. There's a category button on the right side of the wheel - press that button and the left half of the screen should display different categories of sounds like: keyboard, organ, string brass, etc... Navigate through those with your F1, F2, F3 & F4 keys.
3. On the right side of the screen will be your sounds for that category. You can scroll up and down that list with the wheel or the up & down arrows (located to the right of the wheel). As you scroll through the sounds, you can press the audition button (next to the category button) to hear a sample of that sound.
4. Once you find the sound you want, press the F8 (OK) button.
5. To hear more sounds, press the "prog" button (next to the "combi" button) and follow steps 2-5 again.