Do you have an agent? Because that's the first person you should go to about this.
If not then . . . ask yourself some questions before broaching the subject with your editor.
What don't you like about it? Does it represent your work? Does it look like it fits in with the genre your publisher is marketing to? How does it compare to other covers from the publisher? Sometimes we might not like the look of a cover, but it actually fits brilliantly into a marketing trend so we just put up with it. Sometimes, though, the cover sucks.
If you truly feel that this book cover is going to compromise sales (and trust me, I know of authors who have been very aware and savvy enough to know their cover would do just that), then you need to send a very professional very calm email to your editor. In it you need to explain why the cover doesn't work, and I'd suggest making suggestions on what needs to change. Most preferable would be suggestions that augment the existing cover, but if you want something different then do your research. Send cover examples from books that you like and that are in your genre. Show you've done marketing research on the subject.
This is a very touchy subject, and I'll be honest, most authors don't actually have that great a sense of design nor marketing. But that doesn't mean that you are wrong in not liking your cover. I have a friend who was given a horrendous cover by one of the big six, and sent an email (via her agent) with said content I listed above, and they changed the cover to something beautiful.
However, you should note they might not respond positively. Not all publishers do. My other friend has a cover that actually hinders book sales (it makes the book look like it's a totally different genre), and despite pleading with her publisher to change it, they didn't.
In the end, they get the final word.
I am rather curious about the cover, and feel like I've got a good eye (I visit designer blogs a lot, and have designed covers in the past). Would you like to PM me the link and have me share my thoughts with you? No worried if not, just a friendly offer.