Welcome to the forum!
The status bar can help you know which objects are images. Just select with Selection tool, and look at the status bar. Strangely, for reasons I don't understand, the shadows of the boxes are images. I don't know. I'm not set up to handle EPS, so I could only open the AI version. So maybe it was something about the conversion that created the shadows as images.
Anyway, when you're trying to select box #3, maybe you're selecting the shadow/image, like it is for me. So using Alt + click, you can select underneath something. After you change the color of the box, you'll be able to see the shadow better. And then you could trace the shadow with the Pen tool and create a vector object, and then delete the image.
It actually is going to take a good bit of work, just to change the colors there. Because a lot of them are gradients - very subtle gradients. And most of the sides of the boxes are made of 2 triangles, for some reason. I have no idea why.
Oddly....really kind of bizarrely, they've put the back sides and the bottom of those boxes in the image, even though they aren't visible at all! And they actually have gradient fills! Again, no idea why. It really only adds bulk to the file.
I have to say, I've always assumed that images which are available to be downloaded from the internet must be made by professionals. But the more I try to help people work with those kinds of images, the more surprised I am at how they are made.
