Hello, I am trying to update my Mac, but system saying that I should be owner. I bougth this Mac already 2 years

I bougth this Mac already 2 years...

I assume you bought it from Apple and not from someone else who may have already configured it as theirs.

Try the options described under "Other macOS installation options" in How to reinstall macOS - Apple Support.

Specifically,

• On an Intel-based Mac, if you use Option-Command-R during startup, you might be offered the latest macOS that is compatible with your Mac.

Then,

• If you still need help, contact Apple Support.