I'm using channel 157 for my 5Ghz WIFI, this is a setting in your router configuration so you need to access your router configuration to change this. And make sure your device is connecting to 5GHz, it's a wider band thus faster but higher frequency often means the signal of equal power doesn't go as far. Lower frequencies, travel further but may not be as fast due to lower bandwidth, all else being equal.
So try 2.4 GHz router connection if 5GHz isn't working for you, whichever works best, you'll have to experiment some. I found the large appliances in my home were blocking the signal, a couple routers and extenders connected together virtually to construct the WIFI LAN helped me navigate around the dead zone.
If a neighbor were to make configuration changes to his WIFI, his router signal might interfere with yours and thus you may have to reconfigure accordingly.
Power off other WIFI devices then look in your phone or computers WIFI network to see if your Roku shows up, you won't be able to connect necessarily but if it shows up this indicates the WIFI of the ROKU is functioning, doesn't mean it's connected to the router though.