It may be difficult to position the page number and the running head on the first page and then format them differently on subsequent pages.
Watch this 4-minute YouTube video which explains how to set the format in Word 2013 using Windows.
Source: Evans Library & Learning Commons at Fulton-Montgomery Community College in Johnstown, NY. Shows you how to type your paper using APA format. The video was posted on December 9, 2013.
Tutorial by Terrance D. Jorgensen, Kennesaw State University, Kennesaw, GA demonstrating how to type a paper using APA format on a Mac computer.
This is a 10-min. video.