hi. several of our top hung upvc windows seem to have have "dropped" at the rear of our house and we have to slam them to shut them as they are catching on the casing at the bottom. is this a quick fix or shall i contact a glazing firm? they have child restricted catches on them also (not sure if relevant). the windows are approx 8yo but have been doing it since we moved in approx 3 years ago so may have always done this. thanks.