You can use Decks to switch between sets of Balls you like. To find decks, navigate to your Arsenal and look for the teal Gear bar at the top. Your decks are represented by numbered buttons on the right, and you can switch between your decks by tapping these buttons.
The first Deck is available for free from the start, the second Deck gets unlocked once you reach the Master I League, and you can unlock the third deck with gold.
Once a new Deck is unlocked, it automatically gets set up with Beginner Balls, so make sure to swap them out for the Balls you plan to use!