If you are experiencing low Wi-Fi speed, you should check the following:
Your internet speed heavily depends on your network equipment (router)
Number of connected devices
Connection speed is not solely controlled from your side. The other party that you are connecting to also affects it. It could be that the website you are connecting to has a large number of users and the available speed is divided among them all. Likewise, if you are gaming online and encounter slow speed, the issue might be from the connection and the load on the server where the game is located.
Check your device as it may be running too many apps that connect to the internet at the same time. Some might be running in the background without you noticing it. Check your device settings such as auto-update, sync or back-up, as well as file sharing programmes.