There's probably very little YOU can do other than shout at your ISP.
However, the things to try are:
1) Ensure the speed increase HAS happened by logging into your router and checking the synchronisation speeds on the line.
2) Change your DNS settings in your router to 8.8.8.8 and 8.8.4.4 and see if this helps (you will probably have to reboot your PC to see if it helps).
3) Ensure your firewall on your PC doesn't block DNS requests to t'internet. (not a problem if you're using MS Firewall, but if you're using a 3rd party one you would need to reconfigure it.....or better still junk it for the MS one).
See if that helps?
Mike.