I have CHARTER and I replace my old sb4200 with the new sb6121 . it take about 10-15 minute and I be able to do it over Charter 's automated service . the step I follow : 1 -rrb- Goto -lrb- ... -rrb- and take the speed test a few time . 2 -rrb- make connection on new sb6121 and then connect power . by connection I be refer to whatever you have setup already on you old modem -lrb- router or direct connect to pc -rrb- . 3 -rrb- after new modem boots-up launch pc browser . it should take you directly to Charter install page , but if you be like I it do not - so manually paste this address into you browser -lrb- ... -rrb- 4 -rrb- follow self-help option to replace you cable modem . enter account number off you billing statement and you old MAC address . 5 -rrb- when it be complete it say it will `` attempt '' to reboot you modem to complete the installation process . I wait 5 minute and it never do so I power cycle the modem myself . when the new modem power on it do finally work . internet service will not work until the unit have be reboot so do not skip that step ! 6 -rrb- Goto -lrb- ... -rrb- and take the speed test a few time ... compare result to you old modem .