Importing demo content: missing uploaded parts + duplicating Front Page?

Hi Everybody,
(my totally new site is: www.kibontakozo.hu)

I imported the demo content as written here: https://athemes.com/documentation/sydney/

But there was a mistake during uploading and indicated that could not copy Groups / in part of the demo site under: “All works”).
Therefore I tried it again, but so many files were already existing (or duplicating?).
What can I do in order to have all the parts of the demo site?
May I somehow delete the sydney demo content .xml file(s) and start it again from the beginning? Does the maybe duplicated xml files disturb anything?
And may I change the editor name of “chuck” of the Front Page?
And finally, how to create a duplicated/clone site to this original Front Page?

Thanks you very much in advance!!
Orsi
from Hungary, Budapest