Upgrading Legacy Theme (1.4.2 to 1.28)

Hi all,

I have a client who I need to update their current Answers experience theme from a legacy (1.4.2) to the current theme (1.28). I tried looking through Hitchhikers on the best way to do this, but I couldn’t locate any specific instructions on how to accomplish this on a legacy theme. Any insight or advice on how to do this would be great!