dear friend
on next date of hearing in the case ,accomny the accused in the court without informing him that you are going to with draw the suerty.
make an oral request or written application to the concerned court that you intend to withdraw the suery bond and request the court to discharge you. The accused will be asked to furnish fresh surety.The court may ask you to be his suerty till next date. Please dont agree in any case. Let him be takento judicial custody. The court will discharge you then and their and accused will be taken into judicial custody.