I installed CentOS 7 On Dell XPS 15 9550 but WiFi adapter doesn't work. How can I install the drivers? I read that the solution is upgrade kernel to 4.2. How can I upgrade it without Internet connection ?
If you do not have the new kernel, you need to get it. You did not mention that you have other PC, USB disk, Ethernet cable, USB/Ethernet adapter, but I suggested the easiest solution I can envision. :)
Actually simplest would be to connect your mobile phone to PC over USB and enable Tethering on phone - "Share your phone's mobile data connection via USB".
I use that often, as my phone WiFi sensibility is greater than of WiFi adapter in my notebook, so if WiFi signal is weak, I use phone as "adapter". :)
Edit: RPM packages have dependencies, which are resolved on the fly if you are connected to internet, which is easiest way.
Other is to install all the dependencies manually, from USB or CD or DVD. If you are sure that new kernel has driver for your WiFi adapter, than you can get all needed RPM packages, and install them before kernel, and then install kernel.
Please do have in mind that kernel dependencies could have their dependencies. To be precise, almost everything depends on libc & glibc SO's and such.
Maybe you got just kernel images without kernel headers? That's usually needed.