Hi here i list out some reasons which make your internet slow .They are
1.Outdated web browser.
2.Solid objects blocking the way of wi-fi signals.
3.Other might know your wi-fi password, thus they have access to it.
4.Some softwares install malware on your computer, which eat up alot of bandwitch.
5.Unaware of seeding torrents.
6.Viruses in your computer.
Now here i list out some tips to increase your speed they are
1.Update your browser.
2.Place your router in a better place: Lots of thing can impact the stength the impact of a wireless broadband. All solid objects affect it including, Walls, Doors and even chairs. So it is reccomended to place your router in a high platform such as a bookshelf.
3.secure your network .
4.Use less bandwidth .
5.Frequently scan your computer for virus.....
Then check your internet speed through sites like ScanmySpeed.com ....Sure you will see vast difference in your speed results....