Criminal Law Questions? Ask a Criminal Lawyer.
Different states have different procedures but for the most part it is a judicial process (needs to go through the courts) and therefore you would be best off by consulting a lawyer.
Before you can seal or expunge a criminal record you must qualify. If you were convicted / adjudicated guilty of the crime you were charged with you do not qualify. You must get a dismissal of the case or a withhold of adjudication. In Florida, for example, you can only expunge cases that were dismissed and; to seal a case you must have a withhold of adjudication.
Also, not all crimes can be sealed or expunged regardless of whether the case was dismissed or adjudication was withheld. More dangerous crimes such as murder, aggravated battery, sexual battery, etc., may not be sealed or expunged.
You can only seal or expunge once in your life so if you have done it in the past you do not qualify. If you do qualify you will need to sign an affidavit stating that you have never sealed or expunged your criminal record. You will also have to have your fingerprints taken. In Florida this process can take anywhere from 2-5 months.
The fact that he was sentenced to jail time tells me he was convicted making it very difficult to get the case sealed regardless of the charge.
Also most sexual offense cannot be sealed or expunged regardless of case outcome. It does not seem like he will be able to seal or expunge the case but I would need to know the exact charge to give you a definite answer.