What computer are you using and what OS you are using. Try to reset your modem and router. If you use linksy, you can go to the back of the modem. You will see a reset button use a pen and poke the button. Hold it down for 5 seconds and your modem will be reset. Next go to the linksy website at http://192.168.1.1/ . This is only for linsy users. When you go to go and configure the settings as when you reset the modem or settings will be reset to default. Configure your network with a password. Or you can reset your modem by plugging in and out of the power socket again.
I need more information.
1) Like when is it slow ( A particular day/days )
2) How many people are using the internet when it became very slow.
3) Try using other network and connect to internet, see whether using other network will be slow.
4) Problems maybe a network issue or your laptop/pc problem.
5) Check whether other people using your network is having the same problem.
6) Do a virus scan to make sure no virus is on your laptop.
7) Switch your location to somewhere near the modem and see whether the connection is better.