Word for Windows
To change the running head:
Click APA (or MLA)
Click "Edit the header."
Note: If you do this in an APA style paper it will change the running head on both the title page and the body of the paper.
All other word processing software
Edit the header the way you edit any other text in your document. To get into the header section, generally you double click up in the header section of the screen.
Note: In APA style, if you are not in Word for Windows be sure to edit the header on the title page and again on any single page in the body of the document.