Replacing upvc window hinges

[Gossamer]

Evening,
I've a top hung upvc window which needs the hinges replacing.
I've done it before on smaller windows and side hung ones but this is fairly big and on the first floor.
A little nervous about unscrewing it and bringing it in to swap the hinges. Looks heavy.
Any tips?

 

[sircerebus666]

Second body on the outside holding it or take the glass out