It sounds like you may be eligible to vacate although you don't say how long ago you were convicted. You must wait at least 3 years after completing all of the terms of your sentence including payment of all fines and other legal financial obligations. However, many prosecutors won't agree to vacate any Neg 1 that was an amended down from a DUI until at least 7 years have passed since that is how long they will count as mandatory priors for subsequent DUIs. If the prosecutor doesn't agree than you will need to convince the Judge to do so over the objection of the prosecutor. No easy task and something you will want to have the assistance of experienced counsel to have any hope of prevailing.
Please note that this is not legal advice and does not create an attorney-client relationship. This post represents only the poster's opinion. You should speak to an attorney for further information. The poster is licensed only in the State of Washington. For more information about our law firm and services, please visit my website at www.brodskylawfirm.com. I hope this post was helpful to you. Thank you.
Mr. Brodsky is correct in that this particular situation is fairly complex. This is because there is an ambiguity in the law as to whether you have vacate the neg 1 that was amended from a DUI after three years or ten years. While generally you can file all the paperwork yourself, given the complexity of your situation, you're best off hiring a lawyer.
I agree with Mr. Brodsky. I have even heard of prosecutors who not agree before ten years had elapsed. You might talk to a couple attorneys in your area and see what occurs in your local courts. Many of the attorneys would offer a free consultation and would be able to help you decide if you need to hire someone. The prior possession should not matter if it was dismissed, but talk to a few attorneys in your area.
I think you should ask the head prosecutor of Grant County Angus Lee how he did it because he was able to get it vacated/expuged etc. and his record is I guess clear and he was elected prosecutor?