Trying To Change The Difficulty On This Battlefiel

Hey I am trying to change the difficulty on the shinryu battlefield but it only let me choose the difficulty once, and I had chosen very easy.

I know its changeable, to normal, very difficult, etc. I have tried searching around the internet and the various ffxi dedicated websites and cant find anything on how to change the difficulty to these boss fights? Shinryu specifically "The Wyrm God".

nevermind, i forgot i need merit points to get this