Source: Expanded Psionics Handbook
You can upgrade your psicrystal.
Prerequisite: Psicrystal Affinity.
Benefit: You can implant another personality fragment in your psicrystal. You gain the benefits of both psicrystal personalities. Your psicrystal's personality adjusts and becomes a blend between all implanted personality fragments. From now on, when determining the abilities of your psicrystal, treat your manifester level as one higher than your normal manifester level.
Special: You can gain this feat multiple times. Each time, you implant a new personality fragment in your psicrystal, from which you derive the noted benefits, and you treat your level as one higher for the purpose of determining your psicrystal's abilities.