I entered my immaggine, I saved, but remains the joomla logo, how can I do? thanks

Hi,

that small logo image for site logo in mobile view.
and about joomla logo that appear at your site, that called as favicon, not logo.

to changing it, you can using FTP and replace favicon.ico at templates/socialize/ to new one.

you can use this tool, for generate new one:
www.favicon-generator.org/

Regards