If your spc is al 0's, you can usually call your provider to do an over the air programming which is usually automated, for Cricket its *228. If your spc is not all 0's you'll have to manually update it. The only way I knew what prl to use was bc I saw what was on my phone before I starting cooking it. But here is some info.
You can go to http://corolada.com/prl/ and download most PRL's(evdo and roaming) for free no signup. You can go to http://www.rainyday.ca/~dialtone/ to find what prl you should use. It will also tell you your SID/PID if you don't know it.
Once you find the prl you need just dl it and transfer to sd, open epst, go to prl, press browse, look for it, apply settings and soft reset. And you should be good to go. Make sure you find the prl which supports what you have and want ie. EVDO Rev A & roaming if you have it. Hope this helps