How to Install multiple version of Drush? I have Drush 6 installed in my system.

I need to install Drush 5 too (hosting doesn't support Drush6), how do I install Drush5 without uninstalling Drush6 and use both of them simultaneously, Drush6 for local development and Drush5 for SFTP.
In your .bashrc:

alias drush5=/path/to/drush5/drush
alias drush6=/path/to/drush6/drush


With this, drush5 will give you Drush 5, drush6 will give you Drush 6, and drush will give you whichever of these appears first on your $PATH.

Rename your aliases to suit.