Uninstall Mongo old version and Install new version

1) backup data

mkdir mongodb-dump-oct24-2019
cd mongodb-dump-oct24-2019
mongodump

Above will create a folder called 'dump' within 'mongodb-dump-oct24-2019' folder.

2) Uninstall existing version of mongodb
https://medium.com/@rajanmaharjan/uninstall-mongodb-macos-completely-d2a6d6c163f9

3) Install new version
https://stackoverflow.com/questions/57856809/installing-mongodb-with-homebrew

brew tap mongodb/brew  

brew install mongodb-community@4.0

4) brew link --force mongodb-community@4.0

brew services start mongodb-community@4.0

5) Restore data
cd mongodb-dump-oct24-2019
mongorestore