In order to merge two duplicate customers we will want to begin on the CRM page. You can get there by going to CRM on the menu to the left, and choose Customers from the drop down. Once there, you can click on the Utility drop down up at the top to choose the Merge option under Customer.
This will pull up the Customer Merge pop up, where you can enter in the customer name, company, address or number to select the Customer to Keep and the Customer to Remove.
Once you've made your selection, you can continue on to click on the Merge button, which should bring up a 'Merged' message in green at the bottom of the page after successfully merging the two customers.