I want to have a new website look, can i switch to a new theme?

Yes, this is possible. Doesn't matter with witch theme you started. Be aware that all your customized settings will be lost. With switching to a new theme, you overwrite your customizations. Switching back it will overwrite it again. 

• Tip: Note/copy all customizations to a text file. In any case you need them back again.

More information on "Changing the theme/design (Video)"