I'm a level 56, but my HP is 2500. I was watching a youtube walkthrough and they where maxed out. How do I go about doing that.

There are various ways to max out HP in this game. You can use the Berserker's Howl ability to double it. There are also Garment Grids that allow you to break HP limit. And your HP isn't static. It depends in large part on what Dresspheres you favor. Mascot generally has HP, and there are at least a couple over classes that do as well. There's also an accessory that doubles your HP, and of course, Iron Duke is a great accessory to have to boost your stats, but it requires beating the hardest boss in the game.

2x Crystal Bangles equipped at that level can give you over 6000 HP with a Warrior, 9999 with a Berserker, around 8000 with a Dark Knight, 5000 with a Gunner/Thief/Gun Mage, and 3500 with Black and White Mage.

Basically, if you want extra HP, Crystal Bangles are the way to go; you can win them from blitzball, though that takes a bit of time (5-10 hours to raise a decent team that can actually win tournaments and leagues). You can also find one at Youth League HQ on Chapter 5.

I remember the 'hardest boss in the game'. And I agree, Trema is a Grade-A, no-holds-barred pain in the ass! Yet, this failed to stop me beating his ugly, old, wrinkly ass 6 times straight with Berserker dress spheres on all 3 of the ladies. Furthermore, I found that with the right combination of Garment Grids and other dress spheres, he doesn't have much of a chance. I remember my dress spheres at the moment, but not the grids: Yuna - Warrior, Alchemist, Black Mage, Gunner, Thief, Berserker; Rikku - Trainer, Warrior, White Mage, Alchemist, Berserker, Machina Maw; Paine - Warrior, Samurai, Dark Knight, Alchemist, Berserker, Full Throttle

As far as I remember, the Catnip/Trigger Happy L3 trick worked on Trema, but you have to be FAST.

Or maybe I'm just thinking of Paragon... because I recall that being how I beat Paragon.

Lady Luck/Random Reels/777/Pause was my standard cheaty trick, but that didn't work on Trema. So I just switched to standard tactics - increase HP / use powerful abilities such as Moogle Beam on him.

just protect everyone. haste. then darkeness till he dies.
iron duke will be given +100 to almost everything