>Although I went through the documentation but it didnt seemed to be that clear.
You claim to have Read The Fine Manual regarding upgrading physical standby & did not understand it.
Why do you expect anyone will spend their time & effort reposting the same information here with only a faint hope that you'll understand the same information now posted here?
If you'll post the URL to the section you don't understand, perhaps somebody will attempt to clarify your confusion.
Then again, perhaps not.
You can lead some folks to knowledge, but you can not make them think.
The average person thinks he's above average!
For most folks, they don't know, what they don't know.
Good judgement comes from experience. Experience comes from bad judgement.