To change your email address in Dash, you'll need to create a new account using the new email address.
To set up a new account
Invite the new email address to your Dash account (you can do this if you are an admin, or ask an admin to do it)
Sign out
Follow the link in the email you will receive to set up your new account and sign in
Have an admin delete the previous user account
Things to remember
Your new account will not have access to your previous collections or saved searches
If you were collaborating on anyone else's collections, you'll need to ask them to invite your new user to the collection