A JIRA administrator can change your email address by entering this URL:
https://YOURS.atlassian.net/admin/users/view?username=USERNAME
Where YOURS is your subdomain, and USERNAME is your chosen username.
In that page, simply click on the Edit button from the top-right corner, and change your email address.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.