Titan would need a reduction in atmosphere, and a significant amount of heat. Methane is a powerful greenhouse gas and Titan has bodies of liquid methane. As Titan warms, dramatic changes happens to the environment. The methane boils, trapping more heat from the sun, ice melts filling the low elevations with water, ammonia is another greenhouse gas and volcanoes erupts trapping more heat from the Sun causing the moon to warm up more and more. If microbial life forms like bacteria and algea would use the nitrogen rich atmosphere to convert the ground to soil. After all of this happens algea begins to increase the oxygen level. An introduction of plant life would also be needed.