Reference styles are called Output styles in EndNote. The style you choose will change the way your in-text citations and bibliography are formatted in your document.
You need to select your output style in Word. This output style should match the style you are using in EndNote.
Go to the styles manager on the ribbon and choose Select Another Style:
Styles Manager in Word
This will display the complete list of styles. If necessary, click on the Name heading at the top of the column to sort the list by the name. Browse down to APA 6th, highlight it and click on the OK button, as shown:
Selecting an Output Style