Unfortunately due to the style that's going to be harder to modify than some other prefabs, as you'd need to build up the roof over part of the line to create a larger "box" to convert, for starters. I was thinking something like this, where the lime green is the new roof and the purple would be open mesh to provide ventilation.
I assume you're either full time free ranging or adding a bigger run as well?
Here's the rest of the modifications you'll need:
To turn it from 2 small "boxes" (tiny coop above tiny run) into 1 bigger "box" you'll want to remove as much of the inside coop wall as possible, plus the floor. Take out the old roosts too.
Nests might be able to stay as is, or may need to be relocated elsewhere or replaced - depends on the structure of the coop and how things inside stack up once done.
Run a new roost(s) lengthwise or widthwise across the newly open space, depending on how much roost is needed. Ideally you’d like 12” per bird but 10” can suffice in many cases.
Board up some of the external wire walls so that the roost area is protected from winds and rain. Do NOT fully cover up all the wire, you need ventilation and natural light, so at the very least a few inches under the roofline should remain open. If your climate allows for it, you can leave entire walls open with just the mesh, or make it convertible for the season by covering up open walls for winter, and then uncovering for summer.
Example of a modified prefab:
https://www.backyardchickens.com/threads/my-renovated-prefab-coop.1440258/
