You essentially have two options: (1) Negotiating a new or existing installment agreement or (2) an offer in compromise
To ask for a change in amount, you need a Form 433-D. You can get this and download it from IRS website here : http://www.irs.gov/pub/irs-pdf/f433d.pdf On the 1st page, there is a "Date of increase or decrease" statement, so there is way to decrease your payments
That was option (1) ... Option (2) is an offer incompromise. Here'w what IRS says on that:
An offer in compromise allows you to settle your tax debt for less than the full amount you owe. It may be a legitimate option if you can't pay your full tax liability, or doing so creates a financial hardship. We consider your unique set of facts and circumstances:
They actually have an offer in Compromise pre-qualifier on their site here: Offer in Compromise Pre-Qualifier
They are showing a balance of $40,000 for 2007 & 2009. Paid off 2008, and showing no balance for 2004 - 2006. Do you think they will settle this in an offer in Compromise.
Given your change in circumstances, they might. You CERTAINLY have a good chance of lowering the amount of payment based on BOTH the good record and change in icome