su root as user

[watergrinder]

I was trying to connect to a remote system via ssh. When I run the script from my user account, ssh connects to remote system successfully. If I try running the same script as root, ssh asks for root password as ssh does't automatically login as root (unless I enable it in sshd2_config). I also learnt that su root can be done after logging as user. How can I achieve that in my script? Thanks