Click the "Download" tab and the file is there. The download also includes a PDF file which consists of directions on how to update the firmware as well as screenshots of what to select and what to look for after the upgrade.
My phone did a couple of resets on its own after the upgrade, before the metroPCS screen appeared then the main Android screen appeared a minute or so later.
I sincerely hope this firmware update solves the 1900/PCS band rebooting problem it had.
Please print and read the PDF before attempting the upgrade.