Images Editing Onto A White Background

I require 4 images to be edited onto a white background in order to meet Amazon product image requirements. The 4 images i have are already on a white background, they were taken with the product on white desk. But they need editing in order to meet the following criteria:

- Main images should have pure white background (RGB colour values of 255, 255, 255
- Images should be either 1000 pixels or larger in either height or width, minimum requirement in order to enable Amazon zoom function
- Images must not exceed 10,000 pixels on the longest side
- JPEG format