Why is the flame always in an upward direction?

Hint: The air around the candela is hot during burns of candela then rise hot air because they have low density compared to normal air or lighter than cold air. Further takes place by the cold air surrounding the flame of candela and cold air also gets heated and rises again continuously. This continuous cycle of hot air rises, cold air rushing in that procedure of candela flame. This gets heated by cold air because of the swirling effect that flames of candela make point upward or point direction.

Complete answer:
All waxes are formed with the use of hydrocarbons which contain hydrogen and carbon atoms. When we light a candle then the heat of the flame melts the wax of the surrounding candle on top which liquid wax is drawn up the wick by action of capillary action. The heat of flame is vaporizing the liquid wax and breaking the Chain of hydrocarbon into molecules of hydrogen and carbon. The vaporized molecules convert into flame where they react with the oxygen then produce the heat, light and further formed water vapor (Hydrogen oxide) and carbon dioxide.
The continuous flame is a phenomenon of convection current which gives the shape like that elongated or teardrop. The up and down of flame is caused by earth’s gravity.

Note:
If we look at candle flame there are blue areas in the base of flame and its above that dark orange area and above that the large yellow region, generally these contain the color of heat associated with the candle flame. The rise of water vapor and carbon dioxide crates the blue zone; they are heated approx 1000 degree centigrade.