After my probation ended, was my record supposed to be expunged, if not, what was the point of 4 years probation?

Sounds like you were actually convicted, not put on a deferred probationary status. If so, the purpose of the probation years was simply to keep a short lease on you while not requiring you to be behind bars the entire length of your sentence. Contact the attorney who represented you for further information.

Expungement is a complete removal of a case from your record. This action for a felony charge can only be done seven (7) years after you have completed probation. You may be thinking of what is known as a "402" reduction, which reduces any charge one degree and is usually done at the end of a successfully completed probationary term. It refers to the Utah statute section 76-3-402, which allows for reductions in the record. If your plea bargain was to include this type of reduction, you need to motion the court to grant it, which would move it to a class A misdemeanor on your record. You mention 4 years of probation which is unusual. The standard term of probation is 36 month, or 3 years. If you had a probation violation that extended the probation an additional year you may not be entitled to a 402 reduction.