Changing the Default File Manager in Gnome
Changing from Nautilus to Thunar
Step 1: Download this script to your desktop.
Step 2: Paste these commands in the terminal:
cd ~/Desktop
chmod +x defaultthunar.sh
./defaultthunar.sh
Step 3: sudo apt-get install xarchive.
Step 4: sudo apt-get install thunar-archive-plugin.
Restoring Nautilus as the default
If you wish to restore Nautilus as the default file manager in Gnome, download this script to your desktop and paste these commands in the terminal:
cd ~/Desktop
chmod +x restorenautilus.sh
./restorenautilus.sh
Note: the restoration script will work only if you used one of the above scripts to make Nautilus not the default in the first place.