You can also upgrade your BB through the upgrade link on blackberry.com, without worrying about downloading and installing software on your computer.
Some disadvantages to this are: it takes 2x longer than the manual method (up to 3 hrs), you won't have a copy of the OS on your computer after it's done, and it won't install Desktop Manager on your computer.
It is the easiest way to get your BB updated to the latest official 4.5 OS for your carrier though.
Posted from my CrackBerry at wapforums.crackberry.com