To merge an address, you will need to use the Merge Address option found on the original address.
As an example, we'll say that address 501 has been created in error and needs to be merged into address 499.
Things to consider:
Addresses can only be merged if they are on the same account
Merging an address into another will move everything over aside from invoiced transactions.
Go to the address in question (in this instance, address 501)
Click on the Merge Address option on the left
On the next screen, click on the magnifying glass on the right and select the New Address (in this instance, address 499)
The listings at the bottom will display all the items which will be moved over
If you wish the original address to be deleted after the merge, leave the Delete Old Address ticked at the bottom
Click on the Merge button at the bottom of the screen.
The system will move all the listed items from address 501 to address 499. Address 501 will then be marked as deleted if the option to delete was left in place.
Important: There is no option to choose or exclude contacts when an address is merged, these are left as is during the merge.