I've look everywhere, I need to know how I can change my delault email?

What do you mean change the default email? Change the reply to address?

Never mind I figured it out. When go to compose email it comes up use default email. I wanted to chage it.

If you have multiple email addresses configured via the BIS, you can set the default from Options->Advanced Options->Message Services under Messaging(CMIME) select the email address you want. That will be the default when creating a new message.