Check out
this thread about the upgrade exam. Hopefully it'll clear up some of your questions.
If you already have the 1.2 certification, and decide you want to upgrade,
you should simply take the upgrade exam. There's no need for you to take the full 1.4 exam. But make sure you check out this
thread, it discusses the value of taking the upgrade exam:
Anyone taken the upgrade exam yet??? (basically... it might be a better idea to take the
SCJD exam instead of upgrading to 1.4 ....)