To zoom, on a computer, you will need to use a mouse wheel to scroll in (zoom). On a phone, you can use your fingers to zoom in on the photo.
Please note: if you see this low res photo warning, you will not be able to zoom in on your photo.
For reference, here is how you zoom in on an Apple mobile device (photo credit - Apple):
In Safari (on a mac), if you have a newer trackpad, you will zoom in by using two fingers on the track pad like below:
For editing the color or details of a photo, we recommend that any photo editing be done on your local device before uploading the photo for ordering.