How to update passphrase in keychain in mac?

Hi

how to update passphrase in keychain in mac??
while i am trying to do ssh forwarding i am unable to get passphrase update details.

bash-3.2$ ssh-add -K ~/.ssh/cdh55.pem
Identity added: /Users/jagadeeshyadav/.ssh/cdh55.pem (/Users/jagadeeshyadav/.ssh/cdh55.pem)

because of this i am unable to login from one instance to another in AWS.

can you please help??