So I have tried typing the keys that are next to the variables. I also tried holding them down as you stated. But it never lets me alter the value. Because I can not alter the value I can not adjust the strength of the tower. Which fundamentally defeats the purpose of the game as you outlined in the description. Perhaps there is some browser limitation here. I am not sure. Though I kind of doubt that being the case I see it tell me which key is being pressed and or held down.