Change autoresponder emails on business website

This is a REALLY easy project. We have a couple of contact forms on our website. When a user submits, they receive an auto response. We would like to change the text of these 2 auto-responder messages, but knowing little about coding, we have been unable to do so without messing up the entire page! We will provide the text and access to our servers. (The site is hosted on Yahoo). We just need someone to program the new auto responses, format them correctly, and test them to make sure they are working. We would also like instructions on making text changes in the future.