Is there any specific scripts to upgarde windows client machines from NBU 188.8.131.52 to 7.7.3. Please advise.
You could possibly use the silentclient.cmd script to install client software (silently).
Please see this topic in NetBackup Installation Guide :
Installing NetBackup Windows clients silently
Not script-based, but another option is LiveUpdate where you upgrade all clients in one go.
See: NetBackup LiveUpdate Guide
My understanding Live Update is a Symantec product and not a Veritas product and will be discontinued in NetBackup.
LiveUpdate is still very much part of NBU 8.
All it has in common with Symantec LiveUpdate is the name. The process is totally different.
There is also no indication in NBU Futureplans URL that the utility will be discontinued.