Backup your HD first.
I use Macrium Reflect.
Some day I need to understand Windows 7 and 8.1 restore points, and backups. Advantage to software like Macrium and Easus is you can go backwards, or forwards, or whatever.
Might want to learn how to partition your hard drive, keeping the OS on drive C and the data on another one, say "E".
I have had some recent lessons my self, thought Linux/gparted always works, found out Windows 7 does something "funny" with extended partitions, and then brand new machines with UEFI don't even need extended partitions. Ass handed to me twice within a month (new laptop at home, new box at work). Its on my list of things to go research when I am not wasting time gaming.
Luckily in each case, I backed up the entire HD before goofing with it.
If you know how to burn a CD, I highly recommend Hiren's Boot CD, holy cats, does that have gobs of good stuff on it, including a free version of Macrium Reflect and Easus.
I burn CDs with ImgBurn but there are other apps, Microsoft has one, and it might be included with Windows 7.
You will probably want a second HD or external HD. For external, I recommend Western Digital Passport units, they get power for the drive over the USB instead of a that goofy wall wart stuff or lay around brick power supply, man is that nice, I will never buy another external HD that does not work that way.