Read all to understand
a) Upgrade panel:
1. Where can you find it?: Below the pets panel
2. What is there?: 2 boxes where you can put a damage/defense book with a weapon/leggins, armor, helmet or shoes.
3. How does it work?: You press the first book and it will show your inventory from where you can choose a damage book or a defense book. If you choose a damage book you will only be able to choose in the next box weapons and if you choose a defense book you will only be able to choose an armor/helmet/leggings/shoes. When you chose the armor/weapon, etc. you will see above the space between the boxes its current max level and its max level after the upgrade. Every upgrade will have a success chance of 99%.
b) New books:
1. Damage book:
X1. Where can you find it?: Only in the book shop
X2. Price: 500.000 in-game money
X3. What does it add when you upgrade weapons with it?: +1 minimum damage and +1 maximum damage for the weapon. It also makes the level requirement for the weapon higher with +5 levels.
X4. Why so expensive and adds that less?: Because it seems that weapon damage is multiplied by your character's damage stat (power/range, etc.) so it would be too op to cost 100.000 and make the max level higher with 1 level or 2.
2. Defense book:
X1. Where can you find it?: Only in the book shop
X2. Price: 100.000 in-game money
X3. What does it add when you upgrade armor/helmet/etc. with it?: +2 defense and makes the level requirement for it higher with +5 levels