In this example we'll be editing our logo.Blogger templates use images stored on other websites so we need to locate the logo image in the Blogger template.Go on your blog's control panel , navigate to template , click Edit HTML then proceed.
Alright now we need to find the logo image.Click Ctrl + F to start up a search.Look for header or logo.Mine was under header.It should look something like this:

I recommend downloading this image and editing it or at least using the original size because some templates might use the default size of a given image without resizing it.

So we head over to tinypic.com or any other image hosting website and get our logo on there.Once it's uploaded click view full size image and right click on it and click Copy Image URL.

We replace the old link with the new one and we can click preview to see how it looks.If you messed something up you can just close the window and do it again.Otherwise if everything looks good just click save changes and we're done!