Hello Whats the best way to delete a sid and add a new one is it simply by moving the new sid over the top of the old sid and closing the disco then checking that plan view matches the chart procedure

I always just select the new STAR and the FMC usually replaces the old one. If it does not then go to the first waypoint of the new star on the LEGS page and click on it (it will move to scratchpad). Then click on the first waypoint of the old star and click its corresponding button so that the new star waypoints replace the old. Mark.