If you are using Adobe Photoshop or Elements try this:
On the menu bar click Image > Image Size...
Enter in a smaller number into the width box, try 900 pixels. It should automatically re-size the height to match the proportions.
Then go to File > Save for Web & Devices...
On the right menu within that dialog box, choose JPEG and set the quality as you see fit. I would try 70. Click Save.
Then try uploading your new file.
Let me know if this doesn't work or something is way different than I described.
Paper Wishes Web Team