Welcome to Apple Support Communities.
Here's what I think you want to do:
Go to Settings, find Store, touch on Apple ID, and select Sign Out.
Then touch Sign In, select Use Existing Apple ID, and enter the correct Apple ID information and password.
The email addresses, I suspect you already found, under Settings, Mail, Contacts, Calendars.
You didn't mention if you're on iOS 4 or iOS 5. My instructions are using and iPad 2 with iOS 4.3.4.
Don't know which iOS I have. Followed your instructions, but it didn't work. iPad always defaults to the misspelled email address which doesn't exist so can't get email to verify so can't get any apps. When I try to change the email, it says I already have a verified ID , which only works online but not on the ipad