It is not possible to merge contacts in your database.
The data in your contact records is complex and contained within a variety of fields. Because of this, it is not possible for the system to safely merge contacts programmatically.
If you wish to resolve duplicates, please refer to this article titled "Removing duplicate contacts".
To keep your contacts organised we recommend exploring the system's grouped contacts and organisation functionality. Read more:
1. Grouped Contacts
2. Grouping Contacts by Organisation and Relationship