How do I get poliwhirl to evolve?

As a Pokémon expert, I can guide you through the process of evolving your Poliwhirl. In the Pokémon games, Poliwhirl can evolve into two different Pokémon: Politoed or Politoed. The method of evolution varies depending on the game version you are playing.

For Politoed: In most games, Poliwhirl evolves into Politoed when traded while holding a King's Rock. You give Poliwhirl a King's Rock and then trade it to another player. Upon trade, it will evolve into Politoed.

For Poliwrath: In some older games, Poliwhirl can also evolve into Poliwrath through leveling up, but this is not the case in most modern games.

Here's a step-by-step guide:

1. Obtain a King's Rock. You can find one in various locations depending on the game version or purchase it from a Poké Mart.
2. Give the King's Rock to your Poliwhirl by selecting it in your bag and choosing the 'Give' option.
3. Find a friend or another player who can trade with you. You can do this through local wireless, online, or in some games, by trading over the Global Trade System (GTS).
4. Trade your Poliwhirl while it's holding the King's Rock.
5. Upon trade, Poliwhirl will evolve into Politoed.

Poliwhirl is the evolved form of Poliwag, as of level 25. Poliwhirl has two choices of evolution - it can evolve into a Poliwrath via a Water Stone, or it can be evolved into a Politoed by trading it with the King's Rock item attached.