You should always stay on the lowest level where you feel any amount of warmth, even a very slight warmth, coming from the BFST - typically, this means starting off on level one.
As your treatments with the BFST go on, you'll notice that the warmth you feel from the BFST will continue to get less and less. This is a good thing! It means that your circulation is increasing.
The way you'll know when you're ready to move up from level one to level two is when you don't feel any warmth, for an entire twenty minute treatment on level one. You should be feeling next to no warmth whatsoever for a whole twenty minute treatment before you move up to level two.
It's very important for the increase in circulation to be gradual, so it's a good idea to take your time moving up levels.
