Open Run,type DCPROMO then click O.K.
Click next. Click O.K.
Put tick at This is the last domain controller in the domain then click next. Again click next. Now confirm deletion by putting tick at Delete all application directory partitions then click next. Type your administrator password then click next. Again click next. Then deletion will take place like this.
At last you will get window like this.
Just click Finish. Restart your computer now. Your Active Directory will be removed now.