It could be that you've reached your download limit for the month.
You could have some viruses.
Delete your cache and cookies.
If you are sharing with someone else, make sure they are not downloading at the same time.
Here i list out some tips to increase internet speed .
Configure your browser so it won't display graphics, animations, sound, video or other multimedia content (see "How to Turn Off Sounds, Pictures or Video on Web Pages".
Surf when Internet traffic is low. Heaviest traffic is usually on weekends and evenings.
Use your cache effectively. "Cache" refers to storage space where your recently visited Web sites are saved. You may need to resize your cache allotment, or you may need to purge your cache periodically. Look through your browser's menus for items named Cache, Temporary Internet files and so on.
Upgrade your modem.
Consult with your Internet service provider to ensure that your modem is configured correctly.
Replace your telephone modem with a fast-access connection such as wave, ISDN, DSL, satellite, a cable modem.
And then check your internet speed using sites like ScanmySpeed.com