Samsung Galaxy Tab 7.7 internal storage has decreased after upgrading?

Is this the available storage? If it is, it may be because your new OS takes up more room out of you total of 16GB. Sometimes, the total storage is the storage that is readily available to the user and not the total combined storage of the whole thing. I would not worry because this is probably it. My iPhone shows 56 GB available but when I plug it in and access the files from the finder it shows 61 GB. I would think that would most likely be why it is showing 12 GB, newer updates take up more space.

Hope this Helps