When you have two or more entries for the same contact, you can join them into a single entry. You can also separate contacts that were joined.
Open the Contacts app, then tap the contact entry you want to join with another entry.
Tap the Menu icon (at the upper-right corner of the screen).
Tap Merge.
Tap a suggested entry (at the top of the screen).
Once entries have been joined, Separate is included in the Options menu to allow you to separate the joined entries.
Open the Contacts app, then tap the contact entry you want to separate.
Tap the Menu icon (at the upper-right corner of the screen).
Tap Separate.
Tap YES (in the dialog box).