First you'd need to find the rows you want to replace within the ActionDefinitions table. This can be done by using this query:
select Target from ActionDefinitions where ActionType = 'Email'
Make note of the SMTPserver, then use that value in this statement to change it
Update ActionDefinitions
Set Target = REPLACE('mail.oldsmtpserver.domain', 'mail.newsmtpserver.domain')
Where ActionType = 'Email'
This will update all the current SMTP values with the new values for your actions.