There's probably a circlip or snap ring that needs to be removed. You have to push down on the fork cap, then pry out the clip. You may need a helper. Keep in mind that the cap is under spring pressure, so when the clip is removed the cap can go flying & hit you in the head or your eye.
At partzilla. 1983 KZ440-A4. diagram reference #92033. 44044-023 CIRCLIP. (no drawing).
There's also a snap ring listed. 92033A --- 92033-1070, but without the diagram drawing, I don't know where the snap ring goes. It may be that your bike has the snap ring & an earlier model or models have the circlip. not sure. ???
1981 KZ650-CSR. Competition, Sports & Road.