Connect your Blackberry to your computer using a USB cable.
Open the Blackberry Desktop Software on your computer and wait until your device is detected
Click on Device and then Update
The software will automatically tell you if there are any updates for your device.
If there aren't any updates available, try again in a couple of weeks.
Another way to do this:
Go to "options" then click on " "Advanced Options"
Click on "wireless update" then "Next" and then "check for updates"
Keep in mind that if you update it this way, you will lose your current configuration, info and contacts.
Finally try by going to the crackberry website and search for a OS 6 download.