Hi M Osinga,
welcome to the PSR Tutorial Forum!
To call up a style, you must be in the Style Selection display. If you are in the main display, press the "D" display button on the Tyros4. Alternatively you can press any Style Category button (e.g. POP & ROCK) as mentioned by Mike. Then use the TAB buttons to navigate to the "USB1" drive and, if necessary, go to the relevant folder to load the desired style.
Best regards,
Chris