Wrong email adress in app store
How do you change a wrong email address that is only used in the App Store?
iMac, OS X Yosemite (10.10.2)
You can log out of an account by tapping on it in Settings > iTunes & App Store on your iPad
If you mean that you need to correct the email address on the account : Change your Apple ID - Apple Support
After updating it (preferably log out everywhere first and back in afterwards) : What to do after you change your Apple ID email address or password - Apple Support