Upgrade Macbook 6,1 HighSierra

I have a 2009 MacBook 6,1with High Sierra 10.13.6. Xcode needs MacOS 10.4 to execute. I want to develop new Apps but can't unless someone can help me upgrade my Mac's operating system from 10.13.6 to 10.14 or later.

If you know something about this, Please help. I can't afford a new Mac and if I can't upgrade this Mac I guess that would be the end of writing new apps.

Thank you,

Cathy S.