I just got my Curtana Atma weapon. After acquiring the weapon you have to go to Mor Dhona and there you can buy books for 1500 mythology to further upgrade them. As for Paladins you can buy 7 books for the sword and 2 books for the shield.

Shield: there are 2 kinds of books, 1 for increasing strength (+2) and 1 for increasing vitality (+2). Completing both books yields you the Holy Shield Animus shield

Sword: The situation is similar to the shield, except that there are 4 different type of books for the 4 attributes. 2 books for strength, 2 for Accuracy, 2 for Vitality and 1 for parry. Completing all 7 books yields you Curtana Animus.

You can buy any book and complete them in any order you like, but you can only have one active book, you must complete all tasks before you can buy the next one.

I dont have 1500 mythology for the first book, so i dont know what tasks are required.