Change image of demo and have bad picture quality now

Hi,
I uploaded Enfold Health demo theme today and wanted to change the 1st image on the right side in the About-page here: https://www.natuerlich-mit-andrea.de/about/

I wonder why the images on this page were uploaded as “HIntergrundbild” (background picture) in the demo. I used everything as default and only changed the impage. But now the image is in very bad quality. Even when I change back to the old image from the demo, it is still now in bad quality.

It has nothing to do with plugins, I uploaded Enfold and demo today and did not change anything beside of my WordPress settings.

Thanks for helping.

• This topic was modified 2 days, 19 hours ago by AndreasWinkler.
• This topic was modified 2 days, 19 hours ago by AndreasWinkler.
• This topic was modified 2 days, 19 hours ago by AndreasWinkler.
• This topic was modified 2 days, 18 hours ago by AndreasWinkler.