Question

Why a flame always points upwards?

Answer 1

Because hot air rises, and flames tend to be hot. Hot air rises because it is less dense at the same pressure, and the pressure in the flame is roughly the same as that in the surrounding air (or water, in the case of Supercritical water oxidation, where flames behave the same way).

Answer 2

a flame always points upwards because flame is extremely hot and thus less dense than air (by routine approximation using the ideal gas law)and thus rises..