The answer depends on whether the change will in any way affect your customer. It's likely that the user interface may be a bit different, but if the functionality is the same and there are no changes in transaction limits or other things that are disclosable under Reg E or Reg DD, you don't need advance notice.
One suggestion, though. With all the buzz about internet security and smartphone malware, etc., it would be a good idea to announce the fact there will be a change to address potential user concerns.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8