Uninstalling Juggernaut Security and Firewall is as easy as going to Extensions -> My Extensions -> Juggernaut Security and Firewall -> Press the remove button.
You can also uninstall the extension on the command line with:
plesk bin extension --uninstall juggernaut
You can re-install the old Plesk Firewall and Fail2ban extensions using the commands:
plesk bin extension --install firewall
plesk installer add --components fail2ban