How to fix upvc glazed window that drops when you open it?

I have double glazing throughout - when you open the small windows at the top of the main window (push out) the whole window seems to drop slightly so when you close it you need to physically pull it up to realign it so it closes - I haven't actually got the strength to close one of the windows like this. Do they just need re-aligning and if so how do I do that. The larger side windows open and shut fine.

Sheils
April 2009