You can change the bonus attributes for a piece of equipment if it says “Can Change Bonus Attributes” near the bottom in yellow. It will also keep track of how many times you’ve changed the attributes on that piece of equipment, as the Crystal Fragment cost will go up as you attempt more on the same piece of equipment. Accessories will require Green Crystals, Crystal Fragments, and Metacells, while everything else will require Blue Crystals, Crystal Fragments, and Metacells. Green Crystals and Blue Crystals can be obtained through the “Hoard Everything” daily, as well as World Bosses and opening chests around the map. Probably the best way though is to farm the World Bosses. Green Crystals can also be acquired from Ranching rank up rewards. Blue Crystals can also be acquired from Farming rank up rewards.
After you have changed your attributes, you can decide whether or not to keep your old attributes, or change to the new ones. Make sure you do not just leave the panel, and that you actually choose, or else it will by default go with your new attributes. You can lock certain attributes before attempting to change the attributes with Attribute Lock Scrolls which you can acquire from a B4 Treasure Dungeon.