Check your Judgement and Disposition sheet to see what your sentence was, and then find the corresponding form. The most common forms are Act 346, Community Punishment (Act 1460; there is one for felonies and one for misdemeanors), Nolle Prosequi, and Arrest Only.
You are not eligible to seal your record if you have three or more felonies. However, you are still eligible to apply for a Governor's Pardon. The application and instruction packet for a Governor's Pardon can be found on the Department of Public Safety website. If you are seeking to restore your gun rights, use the same pardon application. There will be three options on the second page indicating what will be restored by the pardon if successful. That is where you can choose to pardon your convictions or restore your gun rights. Importantly, if you were sentenced under Act 346, you do not lose your gun rights.
Notaries that can sign your petition can be found at many places, such as banks, car lots, courthouses, and law offices.