Ubuntu can certainly be installed as a second operating system. However, and I must say this at this point, you should have a little technical knowledge for this or at least consult someone who knows something about it in order to implement the so-called dual boot correctly. Memory is neither expandable nor replaceable. The chips are permanently installed and there is no further memory bank for expansion.

Hey, Tastaturlayout / Keyboardlayout CH

No, there is not. There are various series (especially from HP and Lenovo) that offer a combination of Win7 preinstalled and Win 8.1/10 upgrade.

According to [1] which also lists the laptop under the manufacturer no. 9343-9362 (and that's why I assume it's the same model), a Dell Wireless 1560 card is used (tab "Techn. Details" under "Wireless Controller"). [1] http://www.distribution.ch/en/products/1334794-9343-9362-dell-xps-13-i5-5200u-27ghz-8gb-2x4gb