Not meaning to be a smarta$$, but have you read the instructions?

http://www.castlecreations.com/suppo...s_ed_guide.pdf
(See page 30)

Leave it on the default Auto-LiPo setting (2.) It will detect the number of cells and cut the thing off when the pack reaches 3v/cell (12v in the case of your 4S setup.) If you wanted to you could use setting 6, but I see no reason to.

It is important to note that the ESC is just averaging the voltages so you should try to make sure all the individual cells you are using are pretty closely matched.