First of all you can easily change your play settings. When you start the game, you can choose to start Legend mode, Free mode, Adventure map etc. Scroll down till you see SETTINGS. From here choose GAME SETTINGS and then choose BUTTON CONTROLS. From here you can change the mode to Warrior Style.
By Theme you mean in general? This is just to change the layout of your 3DS menu.
If you mean the spin attack: Hold the X button (warrior style) or Y button (Zelda style) and then release it. If you mean in general just swing your sword left and right, use the Y button to attack.