Undo demo install

Hi,
I needed a template from one of the demo themes of Highend – I installed it and it messed up my website – it changed numerous settings (logo, site display, etc.) – is there a way to “undo” what I did?

Also – is there a way just to import the template of a demo, without it overwriting current website settings? I’d like to use one of the templates, but without it messing up what I have already on the site. 🙂

Thanks!