Make sure the shifter is set to the smallest cog (front and rear), pull the hood away from the bars and over the small gear change lever. Cut the old cable and push it towards the shifter, you’ll see it come out underneath to the outside of the brake lever. Then feed in new cables. The bugger bit is getting it to go through the cable guide in the top of the lever (and out into the outer cable). Take care at this point, make sure only enough cable is showing to go round the guide and into the hole leaving the shifter into the outer cable, then get something to push down on the end of gear cable to guide it into the little hole.
Does that make sense?! 😕
Also, make sure when feeding new cable into the shifter that the cables are actually going through the cable stop. I thought I’d **** one of my Super Record shifter mechanisms but it turned out I’d missed the cable stop and fed the cable up the side of it. When I tried to shift from inner to outer rings at the front there was a loud clip then nothing…..! Cue much sweating and panic until I realised what I had done.