Hello Sam01, if your account is a joint account, we cannot remove one of the card holders off the account. We would need to close the account, and have you apply for an account in your own name, which would produce a new card number.
In saying this, if your account is a 'Primary/additional' account, we can remove the additional card holder from the credit card account. In this case the primary card holder can retain the card number.
To see how the account is setup, please contact us on 0800 275 269, send us a message through Internet Banking, or pop into any BNZ Store and we can check on this for you.