I just started playing a few days ago and have tried most of the play modes. However, in Coop Bot Destruction I cannot get upgrades to work. On the right side of my screen I see the flashing double yellow arrow pointing to the D-pad with the down arrow highlighted. I've pressed it, held it down, and tried hitting several other button combos while pressing the down arrow and nothing would bring up an upgrade window. A friend I was playing with said he was having the same problem so I'm assuming it's not an issue with my controller. I've tried searching through Google to get some answers but all I can find are strategies.
Any help would be much appreciated.