Make sure your pictures are saved a "jpg" file and make sure they are not too big. You can resize your photos using "paint" that is on most computers.
Just open up your "paint" program and then go to file at the top left. Click on "file" and then click "open." Choose the picture you want to work with and open it.
After it is open, you will quickly see if it is too big or not. If it's too large it will be huge on your screen. To make it smaller just go to the "image" tab in paint. Click on it and then hit "stretch/skew."
That will open up a box and make your picture smaller. When you are finished click on "file" again. Then "save as." Save the picture as a "jpg" file. Now you should be able to upload it.
Hope that helps