Why does the flame always rise upwards?

All fuels such as wood, match-stick or candle, contain carbon and hydrogen. When these substances burn, carbon combines with oxygen of the air and forms carbon dioxide. Similarly, hydrogen also combines with oxygen and forms water. Some other gases are also produced. As a result of this burning process, these substances produce heat and light. The burning gases are what the flame is made of. The gases produced during the combustion are lighter than air and so they rise up, as a result the flame also rises upwards. If you lightly blow the flame you will notice that it flickers. This is because the air you blow disturbs. In the absence of any such disturbance the flame remains steady.