You may not need to change anything.
"When you set up your iPhone, iPad, or iPod touch, you use the same Apple ID for iCloud services and purchases on the iTunes Store, App Store, and iBookstore. You can, however, use one Apple ID for iCloud services and another Apple ID for store purchases (including iTunes in the Cloud and iTunes Match). You will get all the benefits of iCloud whether you use the same Apple ID for iCloud and store purchases, or different IDs for each."
From here > Apple IDs and iCloud