he has a drug and gun charge
Upfront, I must tell you that these types of motions are not generally successful, and often cause judges to react negatively. The first step would be to motion the case up in front of the sentencing judge, who in most cases will be the judge who presided over the trial, and ask for a modification of the sentence. You will have to notify the prosecutor and then “writ in” your son from whatever penal institution he is serving his time in. This is costly and time consuming for the state, so these motions must be well grounded in fact and based on a good faith belief that a modification is justified by law. You will have to cite specific grounds for a motion of this nature, not just that your son wants to get out prison early because he has learned his lesson. You will have to be specific about circumstances which were not addressed during the sentencing hearing — issues that would have mitigated towards a lesser sentence. Even a well grounded motion is likely to cause and unfavorable reaction by the court, and no doubt the prosecutor will object to any modification. Remember, you’re not retrying the case, you are only seeking to advise the court that the sentence should be modified because certain issues weren’t addressed earlier at sentencing. In all fairness, in most cases, this is unlikely to be successful.
The better route would be for your son to avail himself of the programs that are available in most state and federal penal institutions for drug abuse, alcohol and anger counseling classes. Most often, successful completion for these programs will shave time off of the sentence, especially if you are in a state with a indeterminate sentencing scheme where your son has been sentenced to a minimum and maximum amount of time, for example 5 to 10 years.