Try tightening the two screws that fasten the handle to the window. If the handle still feels loose then you will need to replace it. Here is a link to a website that sells replacmeent handles for upvc windows as most DIY hardware stockists don't sell them:
[url]https://www.upvc-hardware.co.uk/index.php?main_page=product_info&products_id=551[/url]
Blakey, February 2010
