garmin cannot update the changes i have made to my email address

Where are you trying to update it? This is the Express forum.

Oups ! I tried with Garmin Connect (Web and Iphone) and with Garmin.com

You can change your email address here: Garmin | Account | Profile - it works for me. If it does not work for you, try with another browser, or on an alternative Internet connection, or from another phone or computer. If nothing helps, contact the Support through https://support.garmin.com