Restoring WordPress Theme or configuration

I started WordPress with one theme and did little bit of work on it but i decided that theme is not what I need. I installed a new theme but it looks like that things that I did just transferred so I deleted some of the posts but still not good. My old theme came with some preset configurations and I feel that even after I changed the theme configurations were still there.

For example the demo of my new theme has banner and navigation but when I installed it, it doesn’t show me those things, my old theme didn’t have banner or navigation bar so I’m assuming its puling setting from old theme.

I’m just trying to start from beginning and want my new theme to appear just like it does on theme demo.

Thank you,