This can be caused by somethings like:
– Cache on server side. In that case you need flush the server cache.
– Browser cache. Probably not but you can try clear your browser cache.
– Check if the new image it’s on the folder “/img”.
Regarding the size of image (the stretched look) you need define the exactly size of your logo company on attributes width and height of <img>. If you want a retina image you need divide the size by 2. For example:
An image with 400×400 original size should have the width="200" and height="200".
If the problem still persists please send a online link of your project for us, so we can inspect your code and help you.