1st Review following things BEFORE YOU START.
(Consider C drive as your Window drive)
1. You have Hiren's Boot CD 10+ version
After download burn Hiren Boot .iso image to a CD using any CD burner.
2. You must have spare space available on any drive other than C drive or external USB Disk for C drive backup. (Check Properties of C drive for used space)
3. You should be aware that Windows-7 usually installs on two partitions i.e. C partition and a hidden partition (system) see image below: