It's actually quite simple and to find out you could have read/watched the ESF manual which is on the main website or included in your ESF directory. And you also could have looked under you controls settings and looked for the ascend key.
But to cut to the chase, by default the ascend button is Z. You need to get your CF bar full and then you can transform. You can also press X to detransform with all the saiyans, picollo, and frieza.