how can i change submitted email address in "tom tom home" to a different one

i have just bought a second tom tom and put in a second email account address to link to new unit however i found this email address was not registered with yahoo as i thought i done and was now not available, so i had to choose another yahoo one. so please how can i change the email address i put in tom tom home to this new one or does it not matter and the unit will still get recognised / updates etc when connected.