Hi Philipp,
I am not with Laminar Research; just a flight simmer.
Firstly have a look at the system requirements found at https://www.x-plane.com/kb/x-plane-11-system-requirements/ and compare your machine.
Many serious flight simmers build a PC equal to or with specifications greater than the recommended specifications to obtain high performance ie frame rates. X-plane, particularly version 11, is resource hungry which generates heat and the computer being used subsequently requires a good cooling system.
Secondly before you contemplate any upgrade download the demo version to ascertain how well your computer will work. Once you setup a flight in the demo version you will be restricted to a set time limit operating from one particular airport (Seattle ???).
The demo version is a locked version of the full software package. If and when you do decide to purchase X-Plane all you need to do is purchase the software and then apply the provided "product key"
Good luck.
Glenn