Want to move content images from a provider to another

I got a blog with over 500 posts, altho they might not seem a lot, some of those posts have a ton of pictures. I’ve been thinking about moving the images (at least the ones used in the entries) from my current provider to maybe Amazon S3, but that would mean having to edit entry by entry manually and updating the new addresses.

Is there an effective way of doing this avoiding the manual process? Maybe something like search and replace all?