There’s nothing worse than brownies that stick to the muffin tins!  In order to avoid this catastrophe, make sure you grease your tins with nonstick spray even if they are nonstick to begin with.  Also, be sure and only remove from the pans once they are completely cooled.   If you are still having a problem, you can gently run a sharp knife around the edges and ease them out.  Or, bake them in nonstick silicone molds and pop them in the freezer.  That way, you can easily press them out.