Installatron may not know about the latest version of ClassicPress, but it shouldn’t have to: you should be prompted to update automatically.
The most likely cause for your site not seeing the upgrade is the recent expiration of a SSL certificate used by a large portion of the Internet. More info about what happened here: Let's Encrypt's root certificate has expired, and it might break your devices | TechCrunch
Try installing this plugin which is intended to diagnose and fix this issue: GitHub - ClassicPress-research/cp-ssl-fix: Plugin to diagnose/fix ClassicPress SSL issues.
We’ll be shipping our part of this fix in ClassicPress v1.3.1, but the other part has to be done by your web host: GoDaddy needs to upgrade the version of cURL that is used by your PHP installation, and/or remove the expired “DST Root CA X3” certificate from your web server.
In the meantime that plugin should help, please give it a try and let us know what it says (send a screenshot). More info about the plugin here: Sorry, we can't switch this site to ClassicPress at this time - #13 by james