1. Right click on the image you wish to resize and select Edit (The photo will be opened in microsoft paint)
2. Click on resize
3. Select Pixels and type in 500 for horizontal, the vertical will be resized automatically in order to maintain the original shape if maintain aspect ratio is ticked
4. Click on File
5. Select Save As
6. Select JPEG option and save.
You are now ready to upload the photo. Follow the steps in the link below: