Use the following PowerShell script to change your farm Passphrase.
Before running this on your server, you will need machine-level administration privileges.
$passphrase = ConvertTo-SecureString -asPlainText –Force
You will be prompted to input a new passphrase. Once you have done so, input the following.
Set-SPPassPhrase -PassPhrase $passphrase –Confirm
Now you will be prompted to confirm your Phassphrase.