WordPress 3.5 update problem

Hi,

I’m using old version of WP. My website is http://www.samsungoledflexible.com/
I have a problem to update WP from prevoious version to version 3.5 .
When I attempt to update it, I get message :Downloading update from http://wordpress.org/wordpress-3.5-new-bundled.zip… and nothing happened.

Do you know how to fix it?

If it is important, I’m using Mystique theme.

Thank you in advance.