Boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and try to delete 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
If that doesn't work while in Safe Mode move it to the Desktop and bring up it's Info pane (⌘+i). In the Sharing and Permissions section make sure you are listed with Read & Write permission and there's an Admin listed with Read & Write. Save changes and try deleting.
