You have to make a potion with a certain special ingredient. You can find those special ingredients when you loot corpses of powerful monsters. I think the first one you'll encounter is the Golem, whose special ingredient gives you the intelligence upgrade. You acquire it automatically when you drink the potion; no resting or selecting talents necessary.
Actually, the first special ingredient comes from the frightener. But I'm talking bout mutagenic potions that give you special talents, rather than bronze/silver/gold points.