Complete noob - want to return to stock topic

Hi,

I flashed CM 11 onto my One Mini M4 back in November, but am kind of fed up with the crashes etc and want to go back to FULL stock, so I can perhaps sell on the phone and get something a little faster
How can I do this? I don't understand which one of the threads is the FULL stock HTC ROM, and some say "flash this firmware first" which I don't quite understand either. Also I wouldn't mind being able to "relock" the bootloader and put the original recovery back on

Thanks