By mistake, I linked an image to the wrong URL.
I corrected the URL into the post locally, but the URL remains wrong online.
How can I have to correct the URL?
By posting your repo here. Your description does not really help understanding the underlying problem 
If the path to the image changed, then change the path in the referring markdown link to the image. Then run Hugo, then upload the changes. Anything differing from that you would have to explain somehow.
From your description I would think you did not run hugo and/or did not upload the changes.
It’s not simple to post the repo here.
I refer to this post: “Studio Legale Fabiano has a new website with Hugo” | NicFab Blog
The first image has the wrong URL (https://https://www.fabiano.law)
I corrected the URL locally as follows
[](https://www.fabiano.law)
Then I deployed again, but the URL remained wrong.
If you are 100% sure that you fixed the link then your website has some caching issues. Either your browser shows an old version or your server has some caching configuration going on that delivers the old version.
Tip1: Start a browser you did not use recently and load the page and see what happens.
Tip2: Open the browser console and look for anything redish. Maybe something does not like what you changed.
If nothing specific is going on here than Tip1 should solve the issue. Some form of caching of content on either side, yours or the servers.
I did Tip1 and the problem remains.
What happens if I delete the entire folder on the server and I start the deployment again?
The following image loads fine on my end:
<img loading="lazy" src="/images/slf.png#center" alt="SLF">
I don’t see any broken images on “Studio Legale Fabiano has a new website with Hugo” | NicFab Blog
BtW, is there any tool to check broken links on Hugo?
Not as far as I know, but there are generic tools online that crawl a website and generate reports about broken links, like this one.
It’s quite strange.
I rebooted my mac to clear the cache locally, but I continued seeing the wrong URL.
Can I delete the local public folder and start the deployment again?
sure. delete.