Locate your router - wireless or wired, they'll both have a power supply. Go to the back of the box, and unplug the power supply from the router.
Wait at least 15 seconds, then plug the power supply back in.
Go to the rear, or side, of the modem - you'll see a power supply cord. Simply pull it out from the modem, and wait 15 seconds, then plug it back in.
You've now rebooted your modem.
Now try uploading.