Your answers by Anita and Edward still do not help. our income will be less in 2018. My return has been accepted. How can I reduce the amount of my 4 es vouchers?

I am not able to access my return. Since our 2018 income will be less I want to revise and lower the amount that has printed on our 2018 vouchers. Can this be done? Or can I simply use the vouchers that printed but cross through the amount and enter in the same amount we paid on our 4 2017 payments?