[Q] OTA for HTC ONE M8 topic

Hi,
First a confession, I thought I was pretty technically competent until entering the world of Android.
I have a HTC ONE M8. I rooted my device to get access to lots of new features, now though I desperately want to go back.
I have followed step by step all the advice of the Unlocker guide.
However whenever I attempt OTA it boots into fastboot. It doesn't update.
How can I ensure it doesn't boot into factboot?

Currently my HTC says in the fastboot page:
RELOCKED
Security Warning
M8_UL PVT SHIP S-ON
Any help to get me back on track would be greatly appreciated.

Thanks