How to install berta without replacing existing site
You can install berta website also in a subfolder:
1) In FTP go to root of your website
2) Create new folder and copy berta files there (the address will be something like www.yoursite.com/new)
3) If you feel your new website is ready simply copy files from subfolder into root (now by accessing www.yoursite.com you will see your new berta website).