It shows that your HiWatch IPC-D120 IP camera uses the E4 firmware.
At that same Hikvision portal page click on the link titled E4.
You will see that currently it lists and offers only one firmware version (V5.5.4) for your camera.
Device Name IP CAMERA
Firmware Version V5.4.6 build 170629
Encoding Version V1.0 build 170104
Web Version V4.0.1 build 170117
Plugin Version V126.96.36.199