Related Questions:
Combine multiple Accounts
Automate Account merging
How can I merge Accounts?
Procedure:
Click Accounts in the left-hand sidebar
Click the name of the Account you wish to merge
Click Actions
Select Merge
Select the Account you want to merge from the dropdown
Click Next
Use the button selections to choose which values you want to keep
Click Merge
The Merged Account column shows the values brought over after merging.
Please note, Merging IS A PERMANENT ACTION AND CANNOT BE UNDONE.