Plain, simple, nice icon theme to replace the Linux Mint Update Manager panel icons. It's intended for Cinnamon, but should work too on other desktop environments (let me know if you try with success).
-Open Nemo (or your file manager) as root
-Make a backup of the original icons, located at /usr/lib/linuxmint/mintUpdate/icons
-Replace the original icons with the desired theme
If you want to see the changes immediately, open the Update Manager and search for updates.
*NOTE TO LINUX MINT 18 USERS*
I can't find where the icons are in this version, stay tuned.
If anyone knows where the icons are, please tell me to add it.