With one click, you can change the citation style of your document (e.g. change from MLA to APA).
EndNote automatically downloads several hundred of the most common styles. If you cannot find the style in that list, select EDIT, OUTPUT STYLES, OPEN STYLE MANAGER. From there you can select GET MORE ON THE WEB. Search for your new style and download it.
This video shows another way to import a citaiton style into EndNote.