[TYPO3-german] old design needs to be replaced with new one

[Leokadia Angela]

I have a website with Typo3 and I want to have a new design. Until i have developed the new design the old website should stay alive. Is there any way that I can use the current installation for development or do I have to do a new Typo3 installation, do my new design development  and adding the new content first and than upload the files to the old website? But even if that is possible how do I update the content so fast? Sorry I am fairly new to Typo3 and I do not know how this should be done. Please help. Many Thanks