It's very easy using the onboard style creator program. You can find detailed instructions at
http://www.psrtutorial.com/lessons/tune/adjStyle/AStyles60Tuning.html This particular lesson was written some time ago, but all the basics are still the same and the steps are easy to follow.
Good luck,
Gary

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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)