deleting apps on iMac

Boot into Safe Mode as an Administrator (How to use safe mode on your Mac - Apple Support) by booting with the Shift key held down and try deleting them from there. Then reboot normally.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

For those pesky apps that don't like to be deleted that way, in Finder, open the "Applications" section. You should be able to right-click the application in question and delete it that way.

see > How to delete apps on your Mac - Apple Support

and/or > https://9to5mac.com/2018/06/25/mac-how-to-delete-apps/

You can not delete the native App’s that are built into macOS.

Are you logged in as the Administrator?