Need help installing Child & NOT lose current theme contents

Hi, I am trying to install your Travel WP theme on an existing website and importing the Child theme content INTO my current content and then adjust to the Child theme.
I have activated the theme, and plugins BUT when I go to “Tools” Import” “WordPress” choose file, I keep getting this error: This does not appear to be a WXR file, missing/invalid WXR version number

I don’t know what to do, where is the WXR file? I have unzipped the file tried a few folders and even tried the zipped files. Which file do I upload Child theme without deleting all my current pages & products and content etc.
Also Visual Composer will Not install no matter what I do, HELP please.

I thought it was going to be easy but my mistake. I have Put up a website under construction page for the time being.