It couldn't be simpler: you click on the set of your choice and it should take you back to its card, including how to unlock all its parts, as well as the materials required and the improvements of some sets. As a reminder, improving a level of armor requires the intervention of a great fairy: for the improvement to level 4, you must therefore have found all the fountains and pay 10000 rubies.
Written by Bastien "Lloyd" Dubosq-Luyer. Translated from French by Millenium.us.org.