In that case you should realize this will be up to the sentencing judge and it is entirely discretionary. You will want to file a Motion for Early Discharge from Probation. In order to increase the likelihood of success you should have a local attorney put this together for you.
Basically it should contain a summation of the conditions you've completed if applicable (4 years, successful drug screens, fines paid, public service done, etc). Next it should include the things you have done to better yourself since the time of sentencing (rehabilitation, education, job performance, social and family relationships, religious affiliation, etc). You want to show the judge that the probationary period has worked, that you are rehabilitated, and that you will not be a problem in the future.
Please reply if I can help further.
Remember to click ACCEPT only when you are satisfied with your answers. This is how we get paid for our time with your questions. I would also appreciate any positive feedback you could provide. If you are not satisfied then please reply to me so I can further assist you or find someone else to help. I am not your attorney. Therefore no attorney-client relationship exists and any communications on this website are not subject to the attorney-client privilege. For this reason, please do not divulge any personal information and use this site only for hypothetical questions. This forum is for general questions and answers and I cannot provide you with applicable law or legal opinions or advice in your jurisdiction. Please seek the advice of a competent attorney in your jurisdiction. While I can answer general questions and discuss general legal principles, I cannot give you legal advice in your state. The internet is a great place to get general information but should not be seen as a substitute for the attorney-client relationship or the services of a good lawyer in your state.