The time to be asking whether you could have expunction was before you were sentenced. The way the law is written, your chances of successful expunction are much greater if the judge states expunction is allowed at sentencing.
If the court allowed for expunction at sentencing, expunction may happen automatically, or you may have to fill out some forms to request expunction. It depends on the court. A petition to expunge may be found on this page: http://www.wicourts.gov/forms1/circuit/ccform.jsp?page=2&FormName=&FormNumber=&beg_date=&end_date=&StatuteCite=&Category=8&SubCat=All.
If you are going to bring a motion to expunge and the court did not allow for expunction at sentencing, you should have an attorney on your side. When to bring an expunction motion depends on whether you are ready (i.e., in the best possible position to ask for expunction); and whether you are ready depends on a number of facts and circumstances that cannot be addressed on a limited forum like Avvo.
Contact local, experienced criminal defense attorneys for more specific information.