You should keep Your data, You want to keep intact on externa HDD, or other HDD/SSD than Your OS is running on, otherwise it won't stay there. Actually it may, if You manually delete old installation and install new one fresh, it doesn't wipe the OS drive, unless You "tell" the installer to do so. But I wouldn't go that way. I'd keep all the data I want to keep on another drive, and I have this habit of mine, when installing new OS, I turn off SATA connectors from drives I don't want to be affected. Had some really bad experience in the past, it dates back to dos and back to format c: /u /s, which is suppose to format C, and it did all the drives. But turning off the drives in bios [disabling the controller ports] should be enough.