Clio 02 plate 1.5dci how to change glow plugs?

I've just had a look and have found the plugs at the font of the engine, near the injectors(?), is it as simple as pulling the covers off, loosening the nuts, and then replacing them?

What will we encounter after we undo the nuts?

Garage want to charge me £100 for the pleasure of them to change all 4 for me, £33.60 if i buy the parts myself!

Thanks!