Check out page 4 of this PDF: https://www.colordmd.com/Assembly%20for%20Instructions%20WPC%20CHROMA%20rev1.PDF
There are four buttons on the circuit board behind the ColorDMD. With the game in attract mode, hold down the one on the far right to enter the menu. Once you see the menu, pressing the same button again will advance to different options (color, brightness, etc.). Advance to dot style - the middle right button will scroll options up and the middle left button will scroll options down. Select the option you want and then press the right most button to save and exit.