If you want use ← ↑ ↓ → and Ctrl as FIRE choose Kempston Joystick.
Keyboard: Left - A, D, G, J or L, Right - S, F, H, K or ENTER, Down - W, R, Y or I, Up/Jump - Z, X, C, V, B, N, M or SYMBOL SHIFT, Pause/Restart - P, Quit - Q