Hi,
It is not "easy" to suggest what to do, because you may want something different than what I'd suggest.
Fact: Installing Windows 8 will wipe out your ability to restore the pc from the manufacturer's image.
For this reason, I recommend you make a backup of the drive or at least the partition where Windows 7 is installed to, using Clonezilla. (Even if it doesn't have the booting files, it's not a huge deal.)
If you take a screenshot of your Disk Management screen in Windows 7, I can outline for you what I would do if it was my machine.
Another idea: After making the backup of Win7 partition, uninstall any 3rd party antivirus and/or firewall. Then simply upgrade the Windows 7 to Windows 8. To do that, copy the entire contents of the mounted .iso to the hard drive. Then run setup.exe in the Sources folder.
If you hate Windows 8 or something, you can then just put the Windows 7 image back to the partition. You won't have any issues with setup though, because we will help you if you run into any funk.