I am touching up my hair color with product 5N goldwell brand and 5A goldwell brand I want my hair color darker which of the two products do I increase and how much to accomplish this?

If you want your over all color to be darker you will need to choose a darker level hair color, if you want to be one level darker switch to level 4 or even 3. The lower the number the darker the color. If you have any grey hair that you are coloring I would suggest using more "N" than "A" because "N" is the only color that will work to achieve grey coverage. Increasing the amount of "N" or "A" you use will not change the darkness of the color.