adding insulation around a window

[Mountain mj]

I am going to add some insulated plasterboard to a room which is not insulated. This will involve stripping back the plaster to the brick, treating it then building it up again due to damp. There is a window but I'm not sure how to tackle the difference in depth when the new insulated plasterboard is in place.
Do I have to replace the window or is there something I don't know about?

I haven't decided on depth of insulation yet as that will partly depend on the answer to the question.

I've attached some photos of where the window currently sits in relation to the wall. The walls are lath and plaster on brick I believe. The window is a standard PVC window.

Thanks in advance for any advice

 

[Mountain mj]

It may be as simple as removing the window surround and replacing it with a larger one?

 

[ronniecabers]

That looks more like trims than part of the actual window frame to me. Guessing it used to be a sliding sash window and someone's tried to replicate the wood work

 

[Mountain mj]

Yes youre correct. It is trim. I used the wrong words. I think it is as simple as replacing the trim. Thanks

 

[ronniecabers]

Yes you could just remove the trim do what you need to do and then put new trims up if you wanted