I am new to intelligent switches so please bear with me.

I want to update my firmware and something just does not work.

The swich is working and I can log in to the switch using Easy Smart Configuration app. 

Selecting Firmware Upgrade uption lets me enter the location of the bin file but whaen I hit the Upgrade Firmware button I get an error message:

Host IP address 192.168.1.xxx and switch address 24.48.158.74 must be in the same subnet.

My swich subnet is 255.255.255.0 and my PC (192.168.1.xxx) is on the same subnet. What is the problem?

My network is as follows Fiber modem => Router (24.48.158.yy) => switch (24.48.158.74) => PC (dedicated IP address 192.168.1.xxx)

In the near future ther will be an additional switch, i.e. Fiber modem => Router (24.48.158.yy) => switch (24.48.158.74) => switch => PC (dedicated IP address 192.168.1.xxx)

but first I need to solve the puzzle with the 1st switch.

Aside from that, the font used in the Easy Smart Configuration app is so tiny I need to use a magnifying glass to read the text.