Change of e-mail address

Due to a computer/password problem I shall be unable to access my e-mail address that I put on my profile in a couple of weeks time. I went onto the profile to change it to one I have now set up but it told me that I was using an incorrect address and put it back to the one I am trying to change. Can someone please tell me the steps I need to use to change it - I know I'm a bit thick on these things so a step by step guide is necessary. Thanks to anyone who can help.