how to reset root password on debian wheezy

During the pc boot up process, when grub boot loader appears press “e” to edit,
find the line which begin with linux and on the end add init=/bin/bash

example: linux /boot/vmliznu-3.2.0-4-686-pae root=UUID=8cbe7996-107b-4d22-9281-f0962e4917dd ro initrd=/install/initrd.gz quiet init=/bin/bash

press ctrl+x to boot, this will drop you on the command prompt

mount -o remount,rw /