If you do not want to lose changes after updating the new version, you can install childtheme.Using Childtheme has some advantages. You can change (Add, reduce, edit, delete) without having any influence on Parentheme when we release an updated version. Besides, it will not eliminate customs you edited.
Moreover, structure of child theme is quite simple. It only includes 2 files that are functions.php and style.css. If you want to edit any file, you can copy that file from a position of parent theme to the corresponding one of childthemeLearn more about childtheme:
https://codex.wordpress.org/Child_Themes

http://www.wpbeginner.com/wp-themes/how-to-create-a-wordpress-child-theme-video/

https://www.elegantthemes.com/blog/resources/wordpress-child-theme-tutorial

You should follow these steps to update the new version and install the childtheme (we take jobmonster theme as an example):

Step 1. Back up all the data:
Go to wp-content> themes> Change name of noo_jobmonster file to noo_jobmonster_old.

Step 2. Update theme
Step 3. Install childtheme

When you open jobmonster package, you will see noo-jobmonster-child.zip. Please go to Appearance> Themes> Let the mouse hover over the another theme, for example, Twenty Fifteen> Click activate> click Add New button> Upload theme> click Choose file> upload Noo-jobmonster-child.zip > Click Install now.

Step 4. After you install the childtheme, paste edited files in the parent theme into the corresponding position of the childtheme

For example, you want to make changes to header PHP file. In parent theme, please see the directory of this file: framework> admin> customizer > css-php

In childtheme, please create a similar directory > paste the header file you copied from parent theme into a corresponding position in child theme.

Note: To avoid losing changes set in Customizer, please export all settings to a file in Customizer> Import/ Export Settings

After you update, please import the file again.