i can't change this picture.

Instruction here under slider management.

Thank you very much worked for me but the problem continues to homepage.

I mean changing the page/about (https://d.pr/i/h99G), but this page( mainpage( https://d.pr/i/fuPf ) does not change.

Are you saying the demo pic in the second screenshot is still there? Because when I visit your site, I do not see it…maybe you need to force a refresh or clear your cache.

I was completely fix the problem. fix the problem by making changes in the properties of the theme.