Hello everyone!
I explain you my problem: I created a group K2 named "Editors" that has all permits except "publish article".
Users of this group can then edit the articles from the frontend, but ,when saving, the changed article is removed from publication even if it was published.
Is there a way to non allow to publish articles, but if you change published articles, they are not removed from the publication?
Thanks ;)

If you want users to be able to edit current documents (that are published), you have to give them publish permission - this is a Joomla ACL setting.

If you only want them to edit what it on the site, make sure they do not have create permission.

Permissions can get quite tricky and overlapping - one setting upsets the balance. If you are still having problems, post your requirements and I would be happy to try to offer some advice.

Thank you Aaron!
My user has "Editor" as a Joomla user and " Editor" as K2 group.
This is the configuration of k2 group:

Send comments Yes
Edit article from Front-end Yes
Add articles No
Edit own articles Yes
Edit all articles No
Publish articles No

So, my user can only edit own articles. When my user edit an article published and save it, tha article becomes unpublished and a mail is sent to the Superuser to approve this modification.
I wish that the article continues to be published even after the change and the change is immediately visible online.
Thanks for your help! :)

Edit own articles Yes - Good
Edit all articles No - This ensures that the user can only edit his/her own articles
Publish articles No - Change this to YES. They won't be able to publish or unpublish other people's articles because they only have permission for their own articles but they need this this to YES in order to keep their articles published.

There is a risk that a user can unpublish their own article BUT if you leave it at NO, ALL articles will be unpublished.

Hope this helps

Thanks Aaron! ;)
I suspected that the problem was just that.
I will change the Publish articles value to yes!