Step 1: Get the CentOS/Red Hat bootable CD/DVD/USB media.And insert the media into system.
Step 2: On booting you will see some options on screen.Use any one method given below:
Select “Rescue installed system” and hit enter.
Alternatively, you can also press TAB key and add the word “linux rescue” and hit enter.
Do not worry, after this all steps are same.
Now please see this video Recover Linux Grub Password
Here my OS version is centos 6.7. If you have an query please feel free to comment below. Thanks....
Related Video: How to Protect GRUB with Password in Linux