grub

howo to uninstall ubuntu9.10 and get rid of dual boot ?

i installed ubuntu9.10 on my PC and works with XP very great. after install grub lead the system startup and i have to choose between ubuntu and xp. right now,here's another version of ubuntu i want to install,so i have to get rid of grub and ubuntu9.10,i tried fdisk /mbr but id doesn't work. so please anyone tell me how to get rid of...