The File name is different according to the BlackBerry model you choose, just in case.

BlackBerry Handheld Software v4.5.0.254 (EastAsia)

Package Version: 4.5.0.254
Consisting of:

• Applications: 4.5.0.161
• Software Platform: 2.7.0.105
• File name: 8100EastAsia_PBr4.5.0_rel254_PL2.7.0.105_A4.5.0.161_Hutchison.exe
• File size: 90.04MB

Note: The Software Platform and Applications version numbers can be found under Options-About screen on the handheld.

• Download: OS 4.5.0.161 for the BlackBerry Pearl (8100,8110,8120), Curve (8300,8310,8320), 8800 and 8820 From Hutchison
• How To: Upgrade your BlackBerry Operating System (OS)

REMEMBER: Install at your own risk. Always make backups before making major changes/upgrades/downgrades to your BlackBerry.