How to transform in Dragon Ball Z Densetsu MUGEN2010 National Day Edition

Press and hold IO for a certain amount of time, except for a few adult Son Goku, or one or two Gohan who can transform, the rest can't transform anymore! I'm new to this too, and I just summarized it today! If you want to break in, use, the 2nd one in the first row, or the Gohan with the sword, it's fine, it's NB!