To merge contacts, go to the Contacts page and select the contacts you want to merge by checking the box to the left of their names. This will open your mass actions, one of which is Options. Click this and select Merge Contacts.
You will be prompted to choose which contact will be the primary and which contact will be merged into it. Once the contacts are merged, the following information will be added to the primary contact, if present on the merging contact.
Properties - If the merging contact is assigned to any property, it will be replaced with the primary contact.
Email Addresses - A note will be added to the primary contact if the merging contact has an email address.
Contact Groups - The primary contact will inherit any group assigned to the merging contact.
Contact Connection - Any connection that the merged contact has will be added to the primary contact.
Tags - Any tag on the merging contact will be added to the primary contact.
Additional Addresses - If the merging contact has an address, it will be added to the primary contact.
Text Messages - Any text messages associated with the merging contact will be added to the primary contact.
Before merging the contacts, click on the checkbox next to "I understand this cannot be undone." After you check that box, a button will appear to merge the contacts.