How to change the email address of servion.atlassian.net?

[Nic Brough -Adaptavist-]

Go to user administration and change the user's email address.

However, the question makes me suspect you don't mean email address, you actually mean you want your Cloud system(s) to change url.  You can't do this on Cloud, you have to set up a new Cloud system, export from the old one and import the data into the new one.