From what I can see, intelligence improves your fighting ability during auto-play - you move better and dodge/strike at an increased rate. Dexterity improves defence and if you update an armour/acc often, this will go up a lot. HP is accumulated through vitality but you cannot increase this through upgrading alone, it only improves through better vitality stats on better equipment. Other stats increase all of these values too, for example: critical hit rate and damage are extremely important, also damage bonus as well, as these all increase your strength massively. Find the balance between all of your equipment to improve your stats overall, and always have 2 weapons to chose from.