I have a MacBook Air 2015 with latest software of Mojave 10.14.6. I am trying to update to Catalina but when I try it says it require version 10.15. How do I get my mac to 10.15 in order to upgrade to Catalina?

Back up your data, check your applications for compatibility, and click on Catalina.

Catalina and newer won't run 32-bit software; download and use Go64 to scan for it. To check other programs, click here and look them up.

(214163)

Follow the advise pervious previous poster.

It appears you are attempting to download and install an UpDate to Catalina which is Not A FULL VERSION of Catalina

The Only place to get the Full Version is from the provided link from previous Poster.