You can do it without a lawyer and the Harris County District Attorney's website has the form. BUT, you must make sure you notify all the proper parties with your order AND some judges in Harris County (and other counties) will not grant the petitions without a really good reason which they will want explained (along with why you are not the same person who stole, why you stole, what you have done to change, etc.) AND some judges want petitioners to wait for additional periods of time.
So you are aware, you are NEVER entitled to nondisclosure. The judge must find that it is in the best interest of the community and you.
When you file it in Harris County with the filing fee you are given a hearing date exactly 7 days later. You must appear in court that day and present the motion (and whatever evidence the judge wants) along with the proper order if the judge is inclined to grant it.
Although I have answered the question to try to help you, you should consult with a lawyer in your area in person on the matter. In addition, my answer does not establish an attorney-client relationship between us.
Sure you can, but if you don't do it right, you will have wasted your money and time. You must plead in your petition the entities that have knowledge of your arrest and charge to ensure that their records are sealed as well; if one is missed its records will not be sealed.
Additionally, a charge doesn't have to be sealed just because you petition the court. You might have to convince the judge that it is the right thing to do. In that situation, an attorney can help greatly. The minimal amount that attorneys charge for these services is well worth it.
There are attorneys on this forum that regularly answer these types of questions that are your area. Contact one of them (Cynthia Henley and M. Foley come to mind) and see if they can help you.
Although my intent in answering this question is to aid you in the legal process, my answer does not establish an attorney-client relationship in any way. You should seek the advice and counsel of a qualified attorney in your community to evaluate your legal needs and to advise you. No Attorney-Client Relationship is created without the specific intent of both parties.