In the anime, when Pokemons evolve, do they forget some of the moves they learned, or do they simply not use them anymore?

The plural of Pokémon is Pokémon.
I know that in the games, the Pokémon will remember its moves.

Sometimes an evolution will change a Pokemon’s physiology so it cannot do the same moves anymore.

They become more powerful when they evolve so there is no need for the old, less powerful techniques.

According to Bulbapedia, it’s possible for pokemon in anime to learn more than 4 moves (unlike the video game) and use them anytime they wish, although recent tradition dictates that each pokemon can only possess four moves at a time.