All races have transformation prestige classes which let them advance at a much higher rate than normally allowable. Basically for the most part each race will have to gain levels in their particular races prestige class to obtain higher level transformations and more abilities with those transformations

Example - A saiya-jin warrior who has reached 15th level (the prerequisite for ssj1) and who has also met the role playing requirments for the super saiya-jin prestige class, can take his next level, the 16th, in Super Saiya-jin.

All races will have specialty classes like this, but they will differ from group to group on abilities, requirments and even the amount of levels obtainable in each.

Humans
Saiya-jins
Half Saiya-jins
Nameks
Icers
Changelings
Hengeyokai
Biological Androids