Yeah, that's MATE.
Alright, then to launch your file manager as root, just use "sudo caja".
Caja is MATE's file manager.
If that doesn't work then try "sudo nautilus".
Because if you actually are using Gnome, then Nautilus is your file manager.
NOTE: whenever you use "sudo" before a command, you will be prompted for your password. Enter it and your program will launch.