Catholics believe we are judged immediately after we die (Particular Judgement). Some of us will go to heaven. Then there is still the Last Judgement (or Final Judgement). What effect does the Last Judgement have on those who are already in heaven? Will anything about their existence change? The only thing I could find in the article I linked to says that their sins will be made known. Is that all that happens?
Basically, when you die, your soul goes to a place prepared for it, but your body is still here.
So, as was shown with Lazarus and the rich man, you may be in Abraham's bosom, which is a good place, or in Hell, suffering.
But, this is just your soul suffering.
At the final judgement your body will also be with your soul, and you will be judged for the final time, and your body and soul will have the reward or punishment for it.
Whether the place that was prepared for the soul is actually in Hell is not necessarily a closed discussion, as Aquinas states that until the final judgement we will be in Hell, but Abraham's bosom won't involve the suffering that the part in Hell would be.
But, there is also a possibility that our soul will be in Heaven. Either way can be argued, you can read the links below and come to your own conclusion.
Two important things will happen to us at the last judgment that were not already done at our particular judgment. First, although our souls will already have gone to heaven (possibly via purgatory) or to hell, at the last judgment our bodies will be reunited with our souls, to join in their joy or suffering. Second, the last judgment will be public, seen and understood by the whole world, whereas our particular judgment was private, just between God and ourselves. At the last judgment, everyone will see how each of us has cooperated or failed to cooperate with the graces God has given us. Both God's mercy and His justice will be visible to all, and even those who, in this life, worry about how a good God can condemn anyone to hell forever will see that those condemnations are entirely appropriate.