A little late in the day, but this reset method has probably been added to the HX stomp since this question was first asked & answered:
To clear ALL presets (factory & user presets) and IRs - hold all 3 footswitches and power on.
I was running firmware v2.92 at the time of writing.
Usual disclaimers:
Backup your presets before resetting
This procedure will also clear all IRs as well - so make sure you also back them up.