Right, thank you very much Barry. I do hope it's as straightforward as you make it sound like. If I become hopelessly stuck, I'll PM you for the photos.
I've just come back from ACE hardware store & with me I have a slotted screwdriver that I hope is thin & torque-y enough to take those pesky screws off. I'll follow the instructions written by Al Thompson here: http://medfmt.8k.com/mf/infinity.html (about a third of the way down the page).
Would you say the instructions given by Mr. Thompson are correct?