Should not be difficult or dangerous. I swap mine over regularly to test chip developments.
If you want to be really safe disconnect the battery positive terminal first.
Undo the four bolts holding it in. Watch out for the Map sensor at the back tends to fall into the engine bay, and note where the earth wire is attached When it is free remove the big connection (its held by a spring clip at the front and a sort of hook at the back)
As thay say in the Haines reverse the procedure to replace. Dont forget to replace the Map sensor as they don't tend to work very well if left hanging loose in the engine bay.