If you're an iPhone user and updated to iOS 10, you may have wifi issues. My wife and I both did during the last two updates (she had issues with previous update and I had it this time). The solution to both of our problems was pretty easy actually, but not the cheapest necessarily. 

Our Wi-Fi router was getting old, so we had to upgrade either way. So I got a dual-band router, it has 2.4 Ghz and 5.0 Ghz (for faster speeds, especially close up) There are pros and cons of each band, but I won't go into detail here. The number one issue with 2.4Ghz, it's a popular band, therefore is very congested. 5.0 Ghz isn't as busy, but it's not as far reaching. 

I'm not sure what the iOS update did to the phone exactly, but after enabling the 5.0 Ghz band on the router, it's not dropping, always connected and speeds are 4-5 times faster. So that's it, and I hope it works for you too!

Here's a screen shot of the router settings with options to enable/disable the two different bands. Yours may be different.