Background color change for jpeg images

Hi all, I am hoping to sell some clothing on Amazon, and of course will have to upload images of the clothing for customers to see. Amazon has strict guidelines on the exact white color that the background of the images can be. Amazon requires that "MAIN images must have a pure white background (pure white blends in with the Amazon search and item detail pages-RGB values of 255,255,255)." I have 30 jpeg images, measuring 3000 x 4000 pixels and 180 dpi. The background of the images is white cardboard (I placed the clothing on pieces of white cardboard and took the pictures). However they are not the required pure white/RGB values of 255,255,255. Therefore I need someone to change the background of these 30 images to the required white color. I'm guessing one could use photoshop to do this, or perhaps some other image editing software. I tried to do it myself using GIMP, but I wasn't able to capture the clothing outline properly. I'd like to have this completed within a week, or even quicker would of course be better. The project would end (and freelancer get paid) when the jpegs are returned back to me with the corrected white background. Please let me know if you have any questions, or if there's something that I'm forgetting. I've I can easily provide more images as examples if needed. Thanks all!