Step 1: Use a program like pixlr.com to crop and resize your photo
Most homepage slideshow images are 1170px x 400px (if your image is not sized correctly, it will "break" your site.)
Visit Pixlr.com Click Here
Step 3: Click on Shortcuts > Homepage
Step 4: Double Click on the image you want to replace
Step 5: Click on the Browse Server Button
Step 6: Click the upload button
Upload the image (must be sized correctly)
Step 7: Double Click the image you just uploaded to select it.
Step 8: Remove the text that is in the width & height boxes
Step 9: Click OK
Step 10: Click Submit at the bottom of the page to save the changes.