I have a mac os High Sierra version 10.13.6and would like to update to a10.14 so that i can run turbo tax

Back up your data, check your applications for compatibility, and if your Mac is a 2012 or newer model, or a 2010 desktop Mac Pro upgraded with a Metal-capable graphics card, download Mojave through the link provided. If not, it's too old, and your only option without upgrading is to use the online version of TurboTax.

10.13.6 is an OS version, not a hardware model, and doesn't say anything about whether you can upgrade or to what.

(191742)

No. You didn't. You told us what version of macOS you're running, not what model Mac you have.

Click on the  menu and choose 'About this Mac'.

This is what we're asking for:

Exactly what model Mac do you have?