Hello again Chedstog. There are instructions on DRM removal all over the net. But, no matter how justified most of us feel it to be, the practice is illegal and we cannot discuss it here. And I for one, I'm afraid, will not even do so privately.
My wee house is strongly opposed to DRM padlocks. And if an errant third party retailer imposes it by ignoring our demand we have a DRM-free guarantee on our site's store section front page that promises a DRM-free version as an immediate replacement without charge. We ask for no proof of sale or any messing around like that, but we would appreciate knowing the errant store so that we can, if necessary, withdraw our catalogue from it.
Bottom line: Do not buy a DRM ebook.
Luck and best wishes. Neil