You can download and install the latest firmware which is 4.5.0.138 using the steps below:
1. Download the latest 8830 World Edition firmware using this
LINK
2. Install the firmware onto your PC running BlackBerry Desktop Manager
3. Go to c:\Program Files\Common Files\Research In Motion\Apploader and delete the vendor.xml file.
3. Connect your device and open Desktop Manager
4. When prompted select "Upgrade Now"
5. Follow the prompts and your device will be upgraded.
Note: This process can take up to 30 minutes, please do not interrupt this process even if the device appears to be taking a long time to start.