1- set IP@ and name-sever ( or DNS )
2- test internet connectivity + domain name resolution
3- copy the file to the local directory /var/tmp/
4- validate then add file, then reboot the boot
https://support.juniper.net/support/downloads/
...
set system name-server 8.8.8.8
file copy "https://cdn.juniper.net/xxxxxxx/jinstall-ppc-18.4R1.8-signed.tgz?/xxxxx xxxxx" /var/tmp/jinstallimage-ppc-18.4R1.8-signed.name.tgz
request system software validate /var/tmp/jinstallimage-ppc-18.4R1.8-signed.tgzname.tgz
request system software add /var/tmp/jinstallimage-ppc-18.4R1.8-signed.tgzname.tgz
request system reboot
