It is not uncommon to decide to cancel a prenuptial agreement after being married for a while. Be aware that if you just want to amend the agreement, you can do so with a written document signed by both parties. But if you want to scrap the whole thing, there are many different ways to go about canceling your prenup. There are two ways to do it without a court battle---mutual consent, or a "sunset" clause that automatically ends the agreement after a certain amount of time. Otherwise, either party can try to contest the validity of the prenuptial agreement if any of the requirements were not met.
Use the cancel provision included in the agreement. Most prenuptial agreements include a section that dictates the requirements for canceling the prenuptial agreement, which usually involves the consent of both parties.
Let the "sunset provision" do the work for you. Some prenuptial agreements are drawn up with "sunset" provisions, which cause the prenuptial agreement to automatically expire and no longer be valid after a certain amount of time has passed.
Argue the prenuptial agreement should be ruled invalid because it's not in writing or it wasn't signed before the wedding.
Contend that the prenup should be cancelled because you felt "pressured" or didn't read it before signing it.
Convince a court that either party lied or omitted information during the drafting of the contract.
Get the contract ruled as invalid because an independent attorney didn't represent a party, or if the court finds that the contract is so unfair, it is considered "unconscionable."