how to re-install fedora 25 without wiping the personal files

edit

important piece of information missing here: Do you have your /home folder on a separate partition?

If yes, just reinstall without re-formatting /home (set mount point of that partition to /home during install)

If no, backup your data (maybe incl. /etc/), reinstall creating a separate /home (good for future installs), then reinstall. Restore your personal data to /home.

For backup and restore: Do not forget to include hidden .files and .folder (they start with a ., and by default are not visible in Nautilus, hit CRTL+h to display them.)