Hi Olespice,
In general there is no need to change the Apple ID you are using for iTunes on your Mac. You can manage your Apple ID, including changing it and the email address associated with it on this page -
Apple - My Apple ID
https://appleid.apple.com/cgi-bin/WebObjects/MyAppleId.woa/
This article includes instructions on how to change your Apple ID -
Change your Apple ID
http://support.apple.com/kb/HT5621
And this article tells you how to sign in with the correct Apple ID in iTunes on a Mac -
iTunes 11 for Mac: Manage your iTunes Store account
http://support.apple.com/kb/PH12299
This one tells you how to change the Apple ID you are signed in to on your iPad -
Apple ID: What to do after you change your Apple ID
http://support.apple.com/kb/HT5796
Specifically -
iOS 6 and later: Go to Settings > iTunes App Store.
- If you signed out before changing your Apple ID, enter your current Apple ID to sign in.
- If you're still signed in with your previous Apple ID, tap your previous Apple ID and tap Sign Out. Then enter your current Apple ID to sign in.
Thanks for using Apple Support Communities.
Best,
Brett L