Problem with Desktop matching mobile content

[VisibleZoo]

I have a simple Shopify Dawn site full of 200+ digital downloads that I have created. I noticed that all of the images on my mobile are not the same - not the full # of images, and they all carry an"old" watermark that I want to erase. I want what I have created on my desktop to always mirror on mobile. I do not code. 

[Taknify]

Can you share us your store url and if it password protected, share that us too?

[VisibleZoo]

https://www.visiblezoo.com

[Taknify]

The image on your mobile aren't right sized. If you think about it, mostly the desktop has more than 1200*600 px resolution (that is it's width and height), on mobile the screen sizes are no more than 500px (if it is it's not called mobile). You have to use responsive image (same image but show in different resolution for mobile and desktop). Regarding the watermark, it's basically attached on your image. You have to add the product image removing the watermark and reupload it. 
If you need on any of these, my DM's are open. 

Hope this helps answer your question.

[VisibleZoo]

How can I remove all of the images that are on mobile and put them back in after I watermark them (on desktop)? The ones on mobile look ok, they are just old and have old watermarks, and just aren't the right/most current images. There are many more images on the desktop, which is where I create them. I just want both desktop and mobile to mirror at all times. 
All of my images are square, large size download is 2500x2500px, small size download is 600x600 px.