How to enter the second Jhana?

I know you must abandoned applied & sustain thought. Getting rid of applied is easy it's gone once the first Jhana is established. But how to you get rid of sustain thought? I have ready many books & articles but i don't understand them to well. They say once you reach the 1st Jhana review them and see how gross the first really is. But wouldn't that break concentration & push me back to square one?