Unfortunately I don’t quite understand what you mean. Please provide some more details about the issue, maybe some useful screenshots.
Do not edit demo content itself (posts for example), in case you decide to switch demos this will be lost. Every imported post will be removed, the website will be as it was before installing the demo.
You should replace the demo content gradually with your own. Menus, categories, logos content in blocks
In case of settings or modifications not saving properly, please check the theme system status parameters
Ask your hosting provider to increase the parameter values if needed. Insufficient resources can cause such issues.