From the backend of your store… Search or use the category tree to bring up desired products. > Use the number of product shown to increase to max allowed > Use Bulk Actions: select all non discontinued items feature at top right of page > Then use the Bulk Actions Action - Edit Details > click Ok for the you have multiple items selected pop up > In the next pop up window look for royalty information > change to desired percent > click I have the right… and OK. The changes should/will take place on or shortly after the 20th of the month.
For site wide you have to go to your accounts settings page. There is an area where you can adjust ALL your store percent. It can’t be done store by store. I don’t recall exactly where it is in settings, but it is there. I can poke around a bit if you can’t locate it… or someone else can chime in…