Found this thread: [URL]  and realized that I too had Cisco VPN software installed before trying to upgrade. Rolled back to 8.1, uninstalled the software and now WiFi is working.
Hi, Today I've updated my beautifully working xps 13 from 8.1 to 10. I feel like it is slower than previous especially graphics, Wi-Fi is not working, and after I close my laptop and open, Windows is starting slowly from hibernation. I have focused on Wi-Fi problem and tried some chipset drivers reinstall. Device manager was showing that device is working properly. I have even deleted adapter from  device manager and Windows gave me some default one. I'm sure I'm not in airplane mode and I still Windows says that he doesn't see any network devices. Please help! 
Xps 13 (2015) how to update to Windows 10?