Try this speed test:
http://internethealthtest.org/
It tests your speed to the different Internet backbones separately. This can help determine if the problem is your ISP (slow speeds to certain backbones), or with your equipment (everything is slow).
If everything is slow, my first suspect would be your router and/or modem. If you have a separate router/modem, try connecting a computer directly to the modem (might need to reboot the modem after to get it to see the computer). Then run a speed test. This will let you isolate if the problem is with your router or something further upstream (modem or cable connection).
If that speed test is also slow, you've got a problem either with your modem, or with your cable company's connection to your modem. Request the ISP reset the modem (which causes it to reassign download/upload frequency bands). Often when a cable company re-subnets their network, your modem can be stuck on older frequencies which no longer work well with the new subnet.