This isn't a "Windows 8.1 Problem", this is a problem with your hardware. Either your network adapter, or your router, or your modem. Could also be external interference, microwaves for example can interrupt a wireless connection. This used to happen to my mom all the time on Windows 7, when she got a new laptop it stopped.
Don't blame everything on the OS.
You should also NEVER be using the upgrade feature to begin with, back your files up and ALWAYS perform a clean install. When you're partitioning, delete both your C: drive and the "System Reserved" drive, then create a "New" drive out of the unallocated space and format the new C: drive.