@anitelassociazione if you don’t have a backup of your site to go cack to, you can disable the plugin by renaming its folder to something else or moving its folder out of the “plugins” folder either by FTP or the File Manager on your hosting account. After that, you can reinstall the stable version and that would restore your website to its previous state.
To download a previous version of any plugin or Theme in the WordPress repository just follow this instructions:
- Search for the plugin in the WordPress repository
- Go to the plugin’s page
- Click Advanced View
- Click the Development tab
- Scroll to the Other Versions section
- Choose the version you want to download
- On the new page, scroll to the bottom and click Download