[Q] How to flash original firmware in order to get s-off topic

I have an s-on T-Mobile M8 running firmware as follows:

HBOOT - 3.16.0.0000
RADIO- 1.16.21331931.LA24G
OPENDSP- v38.2.2-00542-M8974.0311
OS-
eMMC-boot 2004MB
May 8 2014

I have tried downloading all kinds of firmware files, renaming them to 0P6BIMG.zip and then running them through hboot. Everytime, they say that it is the wrong zip file.

I want to upgrade to one of the many lollipop roms, but when I do, I don't have wifi. I assume this is because I don't have the right firmware. So, how do I get the correct firmware flashed onto my phone with what I currently have?

Thanks for your help!