Hi,
Thanks for contacting us.
Normally, there will have a notification for updating our theme on your website. However, there is some reason why you cannot receive our notification. Mostly, it is the conflicts between your server and our server.
In case, you can update it manually by going to ThemeForest market then download the newest version of Jobmonster theme. After that, delete the older version form your website then upload the newest version via WordPress or FTP.
If you changed your source code or language files, please backup it to your computer or you can use the Child Theme to write them. We also attached a blank Child Theme so you can install it. Please refer to this article to learn how to use Child Theme: https://themefuse.com/child-themes-what-they-are-how-to-use-them-and-why/
Best Regards,
NooTheme