A very pragmatic method, if you know the behavior of the circuit, is sizing the transistors with a W multiple of Wmin (L is minimum, if there aren't particular reasons), making a coarse sizing. Then you can adjust (in function of your constrains) the aspect ratio with parametric simulations using cadence.
Why?i need to change the aspect ratio in that circuit i dont want it to be 10/2 and 3/2... i want it different..
Depends on your requirements!how to calculate it??? and what are the values i should assume???
Lot of questions and no details from your side. I'd think you better study the design books!and please mention which value has to be calculatead using equations???:-?