Available update 1.5.0 notification is for the Agama theme only (free). Agama-Pro theme 1.5.0 update has not been released yet.
If you modified any theme file, that file will be overwritten when the theme is updated. If you want to modify theme files, use a child theme instead.
Using a child theme lets you upgrade the parent theme without affecting the customizations you’ve made to your site.
Also, in case you want to create a child theme from an existing theme without losing the configuration, I suggest using a Child Theme Configurator plugin.
Please check the following post: