You're browsing the GameFAQs Message Boards as a guest. Sign Up for free (or Log In if you already have an account) to be able to post messages, change how messages are displayed, and view media in posts.
You also need to pass certain point of the story. You will get an annoucement saying you can level up your element in the lab. To upgrade you need the fill up the exp, required elements and hunter level.
For leveling up to lv3 and lv4, you have to sacrifice 1 lv2-and-above weapon. The sacrificed weapon will give new level-up weapon a bonus skill.
You can roughly guess the skill by the icons: sword for attack up, shield for defence up, boots for jump up. Other skill include defence against bad status, increased chance of inflicting bad status, regeneration up, medical ring up, so on and forth.
Hope no one lost their weapon accidentally when leveling up......