There is no child theme for any demo, these are built using the default wplms theme only.
If you want to change to demo 6 then refer this tip:
https://wplms.io/support/knowledge-base/installing-demo-1-without-sample-data/
Follow the same steps but with demo 6 plugin.
But I need delete Buddypress sidebar on my website. This what i found on your forum is: https://wplms.io/support/forums/topic/making-group-pages-full-width/
how to made it if I have not child theme?
If you are not using child theme, then you can use blank child theme.
You can get the blank child theme from the wplms package from themeforest.
Simply upload the blank child theme in your themes directory and then activate the blank child theme.