Cooker hood installation

[jack_diy]

Hi,
I want to replace the integrated cooker hood with the chimney style one. I thought it should be a simple work, but I get stuck at the beginning - remove the old one..
As shown in the picture, marked red there is wood board around the flue, I have to remove it first then can disconnect the flue, and power, then remove the hood.
But there's no screw on the surface, so I suspect it's screwed from inside. But there's no space I can get inside to unscrew anything.
Should I try to remove the hood a bit, and disconnect the power/flue at the same time?
Not sure if my expression is understandable, sorry

[jack_diy]

This picture shows the old cooker hood fitting.
If I unscrew left and right sides, I should be able to unhook it maybe?