When do you guys change or alter them? Do you? If you do, why?
I changed some of mine to bring them into line with the brand look I'd gone with.
Some of the early ones didn't conform to the placement of things, and the last 2 in my first series were professionally done and used the wrong font. Another one was just plain boring, and a quick re-colour made a huge difference.
My series 2 was completely re-branded, including 3 title changes. While all of them were professionally done, in the end, 3 of them didn't work, and over time I liked them less and less, and the other 3 were completely different. So when I was doing other cover changes, I redid all 6 of them.
I'm not sure they did a thing as far as sales was concerned, but only 3 of my books have a different look now, and that's a trilogy, where a key element is used a lot ever since. And I'm a lot happier with the covers now.
My first novel has had 4 covers now. I'm not sure any of them have out-performed any of the others. 3 and 4 are a rearrangement of the same cover, where 3 was professionally done, and 4 was me redoing it.