Closing previous form

Question

Friends
I have one problem. In my project instead of forms I HAVE used user controls. and mdiparent and mdichild.I am calling usercontrols on mdichilds panel and mdichild on mdiparent. whenever i want to call another user control  on button click of current user controls previous usercontrol will not close because of this.close() property is not in user control.
plese help