how to update theme correctly

hi, can you please post proper instruction on how to update theme as after all wp updates eventually mobile version menu not showing any available pages to chose from. only noticed it recently as never checked it my self on mobile and not sure how long it was like that but hope update of the theme will sort it out..?

I mean update theme without loosing everything and having to setup all up again.
in other words a-z update guide..
regards

Hi!

Could you send us the functions.php file of the theme via support@smthemes.com, please? And the garage/inc/library.php as well.