I haven't worked on my z1000 in a while but from what i remember you need to take the fuel tank off to access the filler neck and cap to fill the new coolant, just remove the lowest hose that goes to the engine block i believe is on the left side the large one and let is drain out. Flush the system by putting the hose back up fill up the system with distilled water run it for a while (or not your choice) and drain the hose again after that add new coolant.
In the stable: "Studies show geniuses choose green"
2003 zx6r 636 Green 118whp (my baby)
Husaberg fe501 street legal 55hp
2005 Honda cbr600rr
2005 z1000 RawTI
2005 Yamaha FJR1300 Abs Blue