When you make changes, press SAVE. The style is now saved in the equivalent USER folder. So, let's say you edited the style ROCK-BEAT (with the USER button off - factory style found in ROCK). Now when you save it, it saves the style with your changes into ROCK-BEAT (ROCK group but under USER STYLE). To access this style, press the USER STYLE button, ROCK group and select ROCK-BEAT. This way, you can always revert to the factoy version by turning OFF the USER STYLE button and selecting the style again.
Hope this helps.