@stu I"ve only used #PinePhone(Pro)'s but I imagine the process is basically the same.
Download image from website. ( postmarketos.org )
Extract. (I use Ark )
Write image to sdcard ( I use Balena Etcher )
Insert SD card and hold volume down button to boot from that rather than internal storage.
Follow onscreen prompts.
PS, I think @postmarketOS also requires you install #TowBoot first? It's an extra step but not hard. SImilar to what's above. Website is TowBoot.org iirc.
