Hooman: This is something that applied to changing from a multiple members LLC to a single member LLC, and I am pretty sure it will apply to your case as well.
Due to the sensitivity of EIN numbers and registration etc, I believe you are unable to simply "switch" or "cancel" a number, so direct contact with the IRS rep needs to be made.
To change your EIN status you must write or FAX a letter to the IRS facility where you originally filed your EIN and include the following…
Include the legal name of the LLC.
Include your position in the LLC.
Include the address of your LLC.
Include a copy(s) of your Articles of Amendment with the change(s) to your LLC.
Include an explanation of what you did and what you have realized (essentially your YE post) and what you want the resolution to be.
And address the coversheet (FAX) and/or letter to “Attention: EIN Operation”
It’s better to FAX the letter and documents instead of mailing them since it will take an average of 4 days via FAX versus 2 weeks via snail mail to process. If you’re unsure of what address or FAX number to use, it should be on the letter that the IRS sent you when they assigned your EIN, or you can go here
Contact My Local Office and find the local office nearest you.
Hope this at least points you in the right direction, I would call your local IRS office first to ask the best way to do this.
Best
Guy