I looked far and wide for this, and a lot of what I read was a bit confusing. So, here is how to change the default file manager in Ubuntu in an easiest as possible way.
1- Open your terminal
2- Paste this in your terminal: exo-preferred-applications
3- A Preferred Applications window will pop up, so click the Utilities tab, and then locate the name of your preferred file manager in the usr/bin folder.
1- Open your terminal
2- Paste this in your terminal: exo-preferred-applications
3- A Preferred Applications window will pop up, so click the Utilities tab, and then locate the name of your preferred file manager in the usr/bin folder.