how to downgrade back to stock rom

[havieri23]

i recently unlocked my phone, and installed a custom rom. Right now i need to return the phone back to sprint.
i was wondering how do I downgrading back to the stock rom?
do i flash the stock rom first, then flash the relocker? i remember last time when i sold my phone, i couldn't relock my mogul correctly, so i just reinstalled the stock rom, an kept it unlocked.

[sandiegodude]

you need to relock your phone before reflashing it back to stock.