Cloning.
Backup before you do anything. Backup to an external drive.
For cloning (making an exact copy of the entire disk) you need to connect the hard disk to your present computer OR to a different computer and then use a cloning software. There are a few good free cloning software that you can download and run.
There is Acronis (free download from WD's website).
Clonezilla: http://clonezilla.org/
Apricorn (this is what I use):
http://www.apricorn.com/products/software/ezgig.html
EaseUS: http://www.easeus.com/backup-software/ (I have used this) - look for the clone option.
After you clone the hard disk, use the newly cloned hard disk in place of the old hard disk.
Make a backup of the new setup.