I recommend playing this game in full screan. Use the W,A,S,D keys to move. Also use the mouse to aim and shoot. There are 3 upgrades. The first upgrade that says rapid inside of a circle gives you rapid fire but only with 30 bullets. The second upgrade says strong inside of a circle, that upgrade gives you bullets that can take down an invader in one shot but you only have 10 of them. The last upgrade is circle that says sniper on the middle of it. That upgrade gives you 8 bullets that can kill multiple invaders in one shot. Have fun!
