you should get an email from BT about your exchange being upgraded but it can take from days/weeks/months before you get upgraded depending on where you are in the batch upgraded. you will not need a new contract to get the upgrade
if once exchange upgraded and you want to jump the queue you can contact sales and sgree a new contract and get the upgrade - from a few posters recently this does not seem to work as well as it used to and sales just don't help
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