To reset the redhat root password follow the following steps:
1. Reboot / boot the redHat.
2. press any key like space bar.
3.Press a and you and will see following prompt or similar:
grub append> ro root=LABEL=/
4. add single to the above line to enter to single user linux mode and then press enter.
grub append> ro root=LABEL=/ single
5. Linux will go on boot and after a while you will be prompted by similar prompt.
6. type the following command to change the password.
sh-3.01b# passwd <your new password>
7. It will ask you to retype the password after confirm. you can reboot the system by typing reboot.