Firmware 6.39 is set to hit PSPs soon. The update will guide users through the password changing process, getting PSP users up to speed with the new PSN system.
In addition to the password change, the new update will also improve "system software stability." No word yet on when the new firmware will be released, but Sony says it'll be soon.
Don't forget about the Welcome Back program either, PSP users get to pick two titles from a list of four, including LittleBigPlanet, Modnation Racers, Pursuit Force and Killzone Liberation.
Source: PlayStation Blog