They won't try to upgrade your STB instead. Just do as Paul says, & either use the online upgrade, or phone Customer Services (0800 052 2000).
Online upgrade link for SACMs:
http://www.ntlworld.com/data-feeds/e...tierMigration/
Current Upgrade thread:
http://www.cableforum.co.uk/board/sh...ad.php?t=25647