@Ragul Hi and welcome to the Forum 
From the SLE 12 SP5 Release Notes https://documentation.suse.com/sles/12-SP5/html/SLES-all/cha-update-sle.html#sec-update-sle-paths leads to
https://documentation.suse.com/sles/12-SP5/html/SLES-all/cha-update-sle.html#sec-update-sle-paths
You just need to ensure the SMT server has the appropriate releases mirrored to perform an online upgrade.