Since you are on Modern Warfare 3, I am going to assume that you are online. In this case, the easiest way to do this is to delete everything in your cache folder, delete all of your MW3 title update files including the folder in your content files, and then re-launch Modern Warfare 3 using 'default.xex' so that you can easily download the Title Update from the most reliable and easy source. This will cause no harm to your console, as it does not affect your NAND in any way.