A lot of users have multiple Apple IDs and those users are all asking the same question: Is it possible to merge multiple Apple IDs to one single Apple ID?
The short answer is NO, you cannot merge multiple Apple IDs. Further, you cannot delete your unused Apple IDs. What you should do is start using one Apple ID that you prefer permanently.
If you decide to use one Apple ID, you can still access your app purchases (if any) using your other Apple IDs. You can also have all the purchases made using a different Apple ID on one device, iPhone, iPad or iPod touch. To do this, you need to save all your purchases on your Mac or PC and then sync these to your iOS device.
If you are using multiple Apple IDs, you may see this error message: “Sorry…but we can’t find data for you in our system”. If you see this error message, simply clear your web browser’s cookies.
Note: You can use one Apple ID for iCloud services and a different Apple ID for Store purchases (see this article for more info).