[1] There are several methods used to uncap a cable modem, by hardware, software, tricks, alterations, and modifications.
One of the most popular modifications is used on Motorola modems (such as the SB3100, SB4100, and SB4200 models); by spoofing the Internet service provider's TFTP server, the modem is made to accept a different configuration file than the one provided by the TFTP server.
This configuration file tells the modem the download and upload caps it should enforce.
By flooding a modem with faked DHCP packets (which contain configuration filename, TFTP, IP, etc.
Another more advanced method is to attach a TTL to the modem's RS-232 adapter, and get access to the modem's console directly to make it download new firmware, which can then be configured via a simple web interface.