If your intention is to change the Apple ID:
Go to Settings - iTunes & App Store, tap your Apple ID and log out.
If you use the same email address for iCloud, then go to Settings - iCloud, disable Find my iPad, then tap your iCloud ID and sign out there as well.
That done, open this site:
https://appleid.apple.com/us/
Login, then go to Account - Apple ID. Tap Edit there. Below your email address, "Change Email Address" will appear, written in blue. Tap it, and into the popup that appears afterwards, enter your new email address.
A verification code will be sent to the new address. As soon as you receive it, enter it to the fields provided.
If everything works as expected and you can use your new email address as Apple ID, login in iCloud and iTunes & App Store again.