To be able to change the tetrads from T and L shaped pieces to triangles short bars and large squares first complete all practice rounds. Then you will have a red background. Now get an "OK" rating in all modes except practice and multiplay. An "OK" rating is when the game options flashes green. Once you have gotten an "OK" rating in all the required modes the background color will change to green. Finally in all modes except practice you will see a little blue guy. Click on him to change the set.