changing modem settings

[#1]

HELP
how does one go about changing modem setting from @plusdsl12.net to@plusdsl.net ?
Simple to you no doubt, a mystery to me.
J.

[#2]

which router/modem

[#3]

D-Link Modem, does that sound right.

[#4]

Is it a USB modem - perhaps like this http://www.kitz.co.uk/adsl/frogstats.php#17

[#5]

If you follow the instructions on this page but update the connection username, rather than the password it should help you out:
http://www.plus.net/support/security/usernames_and_passwords/dlink_router.shtml

[#6]

  DSL 2640R.

[#7]

Thank you both for your response.
Owing to my limited understanding and afraid to press that last key,have asked my son to sort it when he next calls in.
Again thank you for your efforts.
J.