To increase your stats it's very simple. You need to buy some clear sphere at the monsters arena first. After, you must beat some special monsters in species conquest to get the stats spheres (Hp Mp, Mag def.. etc...) Fenrir, Pterhyx, Hornet, Vidatu, One eye, Jumbo flan (with Anima ;-)), Tanket, Juggernaut and Iron Clad. each time you beat them, you receive 1 sphere or 2 (OVERKILL) Now you have a lot of them, you go to the spheregrid and delete the attribute nodes less than 4. You keep the +4 and with your spheres they'll turn in stat +4 or HP+300 and MP+40. If you want increase your luck stats, your have to defeat EarthEater and Greater Sphere.

With that, you'll be invincible!!!
Hope this help
Maesterdaywalker