After installing Windows 10, some users have reported that their Wi-Fi connection has become erratic.
The first step in resolving this issue is to turn off and on your router; this will likely resolve the vast majority of issues. This is because, like a PC left on for months on end, leaving a router on for an extended period of time can cause it to go 'weird' (a technical term). It only needs to be rebooted every now and then.
If the problem persists, check that all of your PC's Wi-Fi drivers are up to date and correct. To do so, go to Device Manager as usual (search for it in the Start menu). There will be a Network Adapters section, which you can double-click to reveal your adapter.
Select Update Driver Software from the context menu, then 'Search automatically for updated driver software'. Now press the close button. This should take care of the issue.