Ok, it's your data. Simply boot into a live cd, start a file browser as root or use the terminal to rm everything except your home directory then install without formatting the / partition.
You may have to delete some of the hidden files and directories inside /home/<user> too otherwise you may end up with a borked profile and find you can't login to the desktop environment. The best way to avoid this, and here I assume you will want to keep your existing user name, is to rename your /home/<user> directory then copy everything you need into your new /home/<user> directory.
The biggest issue is making sure you delete everything that should be deleted, and of course making sure you don't format /.
Mint Testing Team & Mint Donor #3606
KDE 4.14.2, custom preemptive kernel 3.16.5,
Intel i7 4820K @ 4.7GHz, 32GB Corsair Vengeance Pro
3122MHz XMP, 4 Samsung 840 PRO 512GB SSDs in
RAID0, 6TB HW RAID10, 3 x 24" Samsung UlHD,