Transformation button = Z by default. Upon transforming, you want to do it in a place where people are not fighting or can see you as they may just come up to you and kill you while you are transforming. Also, if you gain enough pl for your selected character eventually you will reach perfect transformation, meaning that it won't take you any time at all to transform at all, you will instantly transform right away (unless your selected character's transformation is one you can't decend from, ie: Cell, Buu, Krillin).