All the demos like demo 1, demo 2, demo 3 etc are built using the default theme only. There is no child theme for this.
If you are using blank child theme then you can convert your website like the demo 2 but if you are using some other child theme, then the whole site will not look like the demo2 because other child themes override the default theme.
Please refer this tip:
https://wplms.io/support/knowledge-base/installing-demo-1-without-sample-data/
This tip is for changing the site into demo1, and using the same steps you can change your site into demo 2, in the above tip demo 1 is downloaded but you have to download the demo 2 plugin and follow all those steps similarly.
Let me know if this helps.