The expungement you're talking about is a dismissal under PC 1203.4. Both misdemeanors and felonies can be expunged if you were granted probation and have completed probation.
Have you finished your probation? If there's still time left but you've complied with all requirements, you or an attorney may seek to have your probation terminated early.
They are quite difficult even for a young attorney so don't feel bad. I have had many clients tell me that they will file it themselves after they hear my quote of $999. Soon after they give it back to me. I encourage you to retain an experienced attorney so its done right the first time.
Many respectable attorneys offer a free consultation. Call around and locate an attorney you feel comfortable with.
The response above is not intended as legal advice since it’s impracticable to provide thorough, accurate advice based upon the query without additional details. It is highly recommended that one should seek advice from a criminal defense attorney licensed in your jurisdiction by setting up a confidential meeting. Moreover, this response does not constitute the creation of an attorney-client relationship since this message is not a confidential communication because it was posted on a public website, thereby publicly disclosing the information, which is another reason to setup a confidential meeting with an attorney.
The best thing is obviously to hire an attorney. If you can't afford an attorney, you should contact the Public Defender Office - they may help you for free or minimal fees. Otherwise, there is good information online and you can try to do it yourself. If it is not granted now, you file it again in the future when you can hire an attorney to help you with it.