Tallima: You'll see them in the game. There's a DLC section in the game and it will connect to the Bioware servers and download anything you check as being activated.
Also, all of your games are automatically cloud-saved on the Bioware servers (I think -- mine were anyway).
enigmaxg2: I was going to ask how this works and found this!
But I have another question: with all DLC I'm practically converting the standard edition into ultimate one?
Ultimate Edition, if I'm not mistaken, came with all but 1 DLC (besides the pre-order DLCs that are now free).
You can buy all the DLC, or buy the Ultimate Edition and get a code to unlock all of the DLC. I'd recommend buying Ultimate Edition if you want all the DLC. The game plays fine w/o the DLC, but it is nice DLC.