Roasting darker reduces acidity. The trick is finding the degree of roast that tames the acidity (to your palate) while also maintaining some of the beans origin/characteristic flavors. By this I mean that if you roast too dark, you might reduce the acidity and end up with more of the darker roast flavors as opposed to the origin flavors that make each bean origin unique.
How are you preparing your coffee, espresso or other brew methods? For espresso, lowering the dose and grinding finer can help tame the acidity. Just keep lowering the dose until you notice the effect on acidity.