1. Download the OS you want for your device
   See: OS Downloads
2. Make sure you have Desktop manager (aka DM) installed. Having the latest version is usually good, though for phones we recommend DM5.
3. Back up your device.
4. Install the OS you downloaded from (1) [It will be in an .exe file. You MUST execute the file and install first!]
5. Delete the vendor.xml file.
   It can be found in:
   C:/ProgramFilesCommonFilesResearchInMotionApploader
   OR
   C:ProgramFiles(*86)/CommonFilesResearchInMotionApploader
6. Delete the second vendor.xml file
   C:\Users\<user>\AppData\Roaming\Research In Motion\BlackBerry\Loader XML
   OR
   C:\Documents and Settings\<user>\Application Data\Research In Motion\BlackBerry\Loader XML
   Note: device.xml should remain inside
7. Plug in your device and follow the prompts to upgrade your OS. Always make sure “third party apps is checked”
   ALWAYS CHECK THROUGH THE LIST BEFORE PROCEEDING OR RISK DATA LOSS!

Step by step Image guide

Do read the TIPS nonetheless before proceeding.

If something went wrong with the upgrade, Simply follow the steps mentioned above if, for any reason, the App Loader is not detecting your BlackBerry. Take out the battery and connect the BlackBerry via USB. Launch App Loader and wait for it to detect the BlackBerry. Sometimes it will display your PIN or say the device is unknown. This will allow you to get to the step in which you choose what apps and settings you want to install on your BlackBerry. Carefully place the battery back in the BlackBerry without unplugging it from the USB port. If fails, consult experts immediately. (Don’t try re-loading more than twice)

If you’re on a BlackBerry Enterprise Server (BES) you should check in with an IT representative before attempting to upgrade your smartphone’s handheld software, because some IT policies can block or partially block a new OS install.