You will have to have the speedometer recalibrated. There is no on-board way to to this. You will either have to take it to a repair shop who has an OBDII scanner with the proper program to recalibrate the speedometer or you can purchase one online and do the procedure at home.
The cost for a scanner that does this is usually well beyond what a DIY type person wants to spend starting at $200+ you can take it to a reputable shop who will charge you between $50 - $100 to do the same thing.
Cheers!!
Monte