How to sign out of AppStore on iPad

I cant download apps from the AppStore as the sign-in box offers me only to enter a password against an old email address. i have forgotten the password and the email address is no longer accessible. I have got a new Apple ID with my new email address and a password that I actually remember, so I need to know how to sign out of the old Apple ID and sign in with the new from the Appstore. I'm a PC person, so this has really got the better of me. In the settings I'm on version 7.0.4. Any help would be appreciated.