Your carrier may ask you to login to download the software, so you might need to create an online account if you haven't already done so.
Once logged in, locate the system upgrades section, check to see if there's an OS version that's more recent than the one you're currently running, and if so, download and save it to your PC's desktop.
To start a new operating system install, you'll need your Black Berry, an Internet-connected PC, a USB cable and about an hour and half of free time—50 minutes or an hour for the upgrade process and 30 minutes or catch-up time afterwards.
Mac users beware: RIM doesn't currently offer the Black Berry Desktop Manager software for Apple computers; however, industrious Mac owners running Parallels and who have a copy of Windows have been able to upgrade their Black Berrys via Macs, though the process can be a bit clumsy.
You should click Next and then on the following screen choose the country in which you're currently located. When the install process is complete, the program will ask you if you want to start the Black Berry Desktop software.
Fill in the check box next to this option and then hit "Finish." Install OS4.5 onto your computer When the Desktop Manager software opens, plug your device into the PC via USB cord.
If you don't delete the other vendor's file, the software won't be able to install the software on your carrier-locked device.
After you've prepared for the changes that come along with a new Black Berry OS, you'll want to begin the installation process.