WiFi router is a device that provides wireless internet connectivity to all devices connected to it (Wi refer to wireless and Fi doesn’t have a meaning). It uses frequency band called ISM (Industrial, Scientific and Medical) defined by the ITU-R (International Telecommunication Union) Radio Regulations and it works on the band 2.4GHz or 5.8GHz.
“ISM” band is even larger than WiFi band and include spectrum starting from 300Mhz ,this band is used and shared by all devices in market (such as WiFi routers, remote controlled toys, drones, Microwave Ovens, Medical devices , etc...) which means they are all interfere with each other.
Interference on ISM band may affect the quality of internet service if you are in area where many WiFi devices are enabled.
Changing your router’s channel can help to reduce interference
Another thing affect WiFi internet service is the signal losses (signal fading) incurred by walls, furniture or any type of blockage inside your home; this will limit the coverage distance of a WiFi router so you need to make sure that WiFi signal is strongly received by your mobile or device to enjoy a good/proper internet speed.
Move your router to a location closer to the center of your coverage area, better reception means better throughout.
Adjust your antennas, if possible, and see what helps. If your house is lengthy designed, alternating between fully vertical and fully horizontal positions can help reach in multiple directions.
Again, due to home architecture, inside obstacles (thick walls) and type of material used, your home may need more than one router to handle it or need a wireless repeater. You can use an old router to serve as a repeater or second access point, to extend your coverage range.
WiFi router is a devices where multiple users can connect and use at same time like:
Your mobile phones and your family mobiles as well
Set Top box
Smart home systems
All connected devices to your WiFi router will share the speed purchased from your internet provider. Ex. If you have 100Mbps speed and WiFi router with 5 mobile phones, 1 smart TV, 2 Tablets and 2 laptops connected and all using the internet at same time then one user speed at that time will be 10Mbps.
Solution to this problem is to reset your password and make sure nobody is using your internet and make sure only your devices connected to your router.
If still internet is slow then connect only one device to check if you are getting speed you purchased, if so then you need to call your internet provider and upgrade your speed.