Funnely enough, I did this exact job on my Clio DCi Thursday.
Injector is easy to remove, crack both the 17mm nuts on the fuel pipe off, remove completely. Pull of leak off pipe, unplug injector (and glow plug as it'll be easier), remove Torx bolt, and then remove the U shaped clamp.
You'll more than likely have to twist the injector carefully to remove it, theres a few flat spots you can get a spanner on, pull injector out.
The copper washer will more than likely stay in the head, theres a special tool you can get to remove them, which makes it easy! but you can also use screwdrivers/a pick tool.
Then clean the face of the head at the bottom, get it as clean as possible, as thats more than likely why its leaking in the first place.
Refit reverse of removal.