The Pokemon Togepi evolves from happiness and not by leveling up. Certain Pokemon species, like the Togepi, only evolve when their happiness quota reaches 220 or more. Togepi evolves into Togetic.
Once a Pokemon that evolves from happiness reaches its happiness quota, it will evolve the next time it levels up through experience or by using a Rare Candy. To raise the happiness level of these types of Pokemon, it has to be part of the player's active party for at least 256 steps, used in battles with gym leaders, the Elite 4 or the Champion. Leveling it up depends on the Pokemon's reaction, through a haircut with the Haircut Brothers in Goldenrod City.