The thing to do is to remove each portlight, one at a time by undoing the hinge bolt. With the portlight removed you now have clear access to get at the aluminium hinge and catch brackets. These are small “L” shaped aluminium parts held in place by a small countersunk screw. The screw I think is made from stainless steel, and with that comes the first difficulty in that they can be seized into the aluminium portlight frame. So probably before doing anything at all you should spray some easing oil, WD40 or similar onto each of those particular screws and leave them for a week or two, topping up the easing oil occasionally. There is a lightweight plastic trim provided around the internal perimeter of the Lewmar portlights, and these should be eased gently away before you start.
Once the easing oil has had chance to work try once only with a cross head screwdriver to remove those screws. If that doesn’t work and they don’t undo easily, don’t try it again. Instead I used an impact driver with a relatively lightweight hammer and was able to remove all of the bracket screws on two portlights only, the screws on the remaining four large portlights were totally unwilling to undo and hence my need to look at alternatives. If you are able to remove those screws on all of the portlights then you can go down the route of spending £1000 if you want. If those screws do not undo then your choices are to do as I did, or to buy new portlights complete with frames.
The new portlight acrylics that Lewmar provide have different size hinge pins, different size plastic hinges and catches as well as those “L” shaped brackets, and the new acrylics will not fit and close using the old brackets.
If you are able to remove the securing screws for those brackets, your next problem will be to remove the brackets from the slot through which they are placed. This is also not an easy task and is likely to make you think of all kinds of uncomplimentary things to say about the way they have been fitted.
New Lewmar portlights should come with a complete new set of those brackets, so don’t worry too much about the condition of the old brackets once you have got them out as the new brackets are much easier to put in place than to remove. I had to resort to using a small file to ease removal of the old brackets on the two windows I replaced with new Lewmar acrylics.
I didn’t mess around with the four remaining portlights and went ahead with my DIY option.
Good luck.