There are lots of free online services that will resize photos for you, but we’ll recommend http://fotoflexer.com/
On their home page, click “Upload Photo.” Then on the next page click the “Upload” button and choose the image you want to upload. Next, click the “Resize” button in the toolbar. In the first field, type in 640 or less (which is the width of the content area) and press “Apply.” Click the “Save” button at the top and then click the “Save To My Computer” button. That will save it to your computer, and from there you can select it and upload it to your PitchMagic site.