Yes, you can change the touch controls, but only when you're in the game. 

While playing, click on the burger menu in the top-left part of your screen (the icon with three lines), then click on 'Controls' and 'Edit mode'. 

This allows you to adjust the size and position of the joystick and the action buttons. Currently, it is not possible to move the buttons individually or choose between a fixed or floating joystick.