How can I access my itunes account from a different computer as I need to cancel a subscription and I am on holiday at the moment

If the Computor you are on has iTunes library go to tunes as if u were going to buy a song or film and you can log into your account. At the bottom of the iTunes home page you should see the user that is logged on usually a email address. Click on it to log them out and enter your own apple I'd and password. You can then update whatever you want and log back out after