If the person you paid was worth even a dollar, they would have made all your customizations using the child theme. The point of the child theme is to protect any customizations that you’ve made: http://codex.wordpress.org/Child_Themes
When you upgrade, you are only upgrading the parent theme, not the child theme.
If they did all the customization in the child theme, then nothing will be “lost”, but depending on what they changed, it might not work. You should have dev/test environment for testing upgrades.
As far as what was changed, each upgrade has a versionxxx.txt file that tells you what was fixed/added. You can download the upgrade from theme forest to view it. Or you can take a look at this sticky topic: https://archived.seventhqueen.com/forums/topic/kleo-updates-change-log
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