I want to update the Os X 10.6.8 to Os x 10.7 or later version , tell me what to do ?

Question

I want to isntall some applications on my mac , that i can't install with my Os x 10.6.8 , so i wanted to update the system to 10.7.4 , but it requires 10.7 version , anyway tell me if i can do anything to update the version i got . thanx in advance