Updating from 13.6 to 13.7.2

What is the easiest way to update from 13.6 to 13.7?

That depends on how you’ve installed Asterisk. If you’ve done it from source then downloading and building 13.7 to match that of your 13.6 build will work fine. If you’ve done it from a package then you could update using that mechanism if 13.7 is available.