You can revert to the previous set of software using the request system software rollback command in the CLI. Rollback fails if the junos-jseries software bundle cannot be found in /var/sw/pkg.
You can roll back only to the software release that was installed on the Services Router before the current release. After you issue the request system software rollback command, the old release is loaded and you cannot reload it again. Issuing the request system software rollback command again results in an error.
To downgrade to an earlier version of software, follow the procedure for upgrading, using the junos-jseries software bundle labeled for the appropriate release.