Try changing wi-fi channels.
If your router supports channel scan, do that and see which channel is furthest away from busy channels.
I'd recommend either channel 1, 6 or 11 if you're on 2.4GHz. 5GHz channels shouldnt matter too much, just leave that on auto.
Try changing channel width. 40 MHz if there's not a lot of channel traffic, 20 MHz if there is a lot of traffic on the channels. Same applies for 80/40MHz if 5GHz works for you.
Restart the router and fiber optic modem (if you have DSL ask your ISP to restart the port on their end).
Move the router away from all large electric appliances, cordless phones and similar devices. Try to make sure it's high up, not obstructed, and in as open an area as possible(don't put it inside a cabinet or drawer).
Get a better wifi router and/or better wifi reciever.
or just use an ethernet cable to solve all your problems