First, You must have pokemons at least two.

go to the PC, right-click the PC.

And Then, drag pokemon that want to remove to the trashcan. 

I'll remove Voltorb. Just click it and drag to the trashcan and click it again.

Now, you have removed the pokemon.

여기서 문법 틀린거 있으면 알려주시면 감사하겠습니다..ㅠㅠ