Go to your ingredient list and click on whichever dried extract you have been selecting for your recipes. You can change the "extract" value for each fermentable ingredient. I'm sorry that I can't help you with exactly what percentage to use, but that is how you change it.
If you don't want to mess with the pre-sets, you can just create a new extract listing to use for your recipes.
Bottled: Atonement Brown Porter