You will need to download the Leopard Docks App for free at http://leoparddocks.com/index.php
Step 1-Go to http://leoparddocks.com/index.php and search and download the dock theme you want to use. I have selected Glossy Black Dock to use.Step 2-
Open the Leopard Docks App.
Select Browse….and search for your downloaded dock theme. It should be in the Downloads section of your mac.
Next click the Change My Dock button
A box will pop up asking you for your password before making any changes.
Your Dock will respring and the new dock will be displayed
Exit the App and you have successfully changed your dock!!