If you have a mouse it's easy, if not its just as easy but you need to be in virtual mouse mode. Hold down L1, then click the joystick R3. You can then use the right joystick as if it was a mouse, with L2 being the left button and R2 being the right button. So, all you do is be in mouse mode, drag the cursor to the upper right corner of the chat box itself. The cursor will change shape. I can't remember if it's a hand or star or whatever, but it will change. Then hold down the L2 (left button on mouse) and drag it out with the stick. You can go up, out, whichever direction you want to go and the chat box will change size as you see fit.