hi everyone, im trying to upgrade my mac os 10.12.6 to the new version (catalina 10.15.3). Every time im trying to upgrade the mac says IO need version 10.15 first and then to upgrade to the latest one. unfortunately Im not succeeding to upgrade.

It sounds like you downloaded a Catalina patch for an existing Catalina installation. To download the actual macOS 10.15 Catalina installer use this article:

https://support.apple.com/kb/HT201475

Or follow @Smokerz' instructions for using Internet Recovery Mode instead.

Just make sure to have good working backups before you upgrade in case something goes wrong or you don't like Catalina. Also Catalina does not support any 32bit apps so if you are using any 32bit apps either upgrade them or uninstall them before upgrading to Catalina.

try and GET or download the full installer which should be about 8.17 GB in size. Don't use the update installer.

Try this: Save your personal data first.