In order to upgrade any of the shell kickers or turtles you have to find T-phone upgrade!! Wich alows you to do that. Press start and look at the map. Can be found in skyskryper basment area(dark purple section on the map), up left corner room. Left side of letter R on the map, 1 room away. Then press start again and twice RB for upgrages. They require lv wich you get by killing enemys. Max lv 16.