Go into settings -> Wi-Fi -> find your network -> press the circled "i" icon next to it.
At the top you should see "Forget this network" (if you are connected to it at the time)
Tap that, then re-add the network and password for it back in.
That should fix it. If it doesn't, try it again only this time standing right next to the router. It might be you have a "dead zone" in your house.
If that doesn't fix it, test your ability to stay connected on a different Wi-Fi network (like a coffee shop network, or the library, friend's house, et al). If you have trouble staying connected to all networks, that would suggest a hardware issue.