Removing spiciness from a dish
For capsicum type peppers (any of the chili peppers including red pepper, jalapenos, serranos, habeneros and so on), you can reduce the heat by cutting out membranes and ribs (which hold the seeds), where most of the capscaicin oil is found.  Of course, you would have to do this before cooking.

Again for, capsaicin, which is fat soluble, having a lot of fat, especially from dairy like cream or sour cream, can help reduced the perceived heat.

Of course, the very best method to control heat from any of the sources is to not put it into the dish in the first place, by reducing the amount of the hot ingredients.