Replacing peanut butter with butter

Your question doesn't say what the replacement strategy is for - baking, cooking or serving spread on toast.
For spreading on toast, use any nut butter or (dairy) butter you like.
For baking or cooking, however, I would avoid butter. It is about 80% fat, 18-19% water and 1-2% milk solids (averages as sold in USA supermarkets). Peanut butter, on the other hand, is slightly lower in fat (72%) but also has carbs, fiber and protein.
For baking and cooking, I would use another nut butter - one of the many ready made and on sale, or something you can puree at home from scratch.