when it comes to substitute goods, if the price of Sprite increases, what will happen with the demand for a substitute good like 7-up

If the price of Sprite increases, the demand for a substitute good like 7-up will increase too, because people will seek for a substitute product to replace Sprite.

Law of demand explains the higher the price of a good, the less people will demand it (or avoid it), and will seek others to replace it.