How to modify a separation agreement

My husband and his exwife signed and notorized a separation agreement that was not incoporated in their divorce papers (it was left out of the fianl documents my mistake however I understand it is still a legal document and binding. Since the papers were signed my husband has lost his job and does not get unemployment benefits- what does he need to do change the amount (remember this is not court ordered) just an agreement between the 2 of them in writing. We completing understand her dilema however he can’t pay $500 a month when he makes $0 right now. Our only income is my income and we are about to have our power cut off and have other bills to pay just to have a roof over our heads- we are living way way below our means, yet meanwhile the exwife is paying more than $300 month for competition dance and paying for an 11 year old to have a new cell phone- We understand the child support is due- we just don’t have what we agreed to all 2 years ago when he was making great money in the auto industry now he can’t find a part time job. So my question is:

[color=#0000FF]Is the separation agreement legal and binding?
What can we do to modify the agreement?
She will not agree to amending the agreement- so is there anything we can do? Does she have to agree? or will he be required to pay the $500 each month regardless of his income?
He also agreed to pay for day care and dance lessons but again he makes no money right now. Will he be required to continue these cost as well?
Can he go before a judge and ask to have the separation agreement modified based on his situation?[/color]

The separation agreement is binding, and the amount of child support contained therein will be presumed to be the amount necessary to provide for the children’s best interests however your husband should file an action to have child support determined by the court, and the court will take his current income and circumstances into account.