Duplicate apps after setting up new Mac

I bought a 2017 iMac 5k 27" and after migrating data from our old Mac Mini, I have many core Mac apps that are duplicated in the Applications folder, like Calendar, FaceTime, Mail, App Store. One of each pair is an older version than the other. I can't delete the older versions because I get an error of "xxxxxx can’t be modified or deleted because it’s required by macOS". Any ideas?