1. Make sure that you have date+time set correctly in your phone settings. Also, you may need to charge your phone to complete next steps.

2. Select Settings > speech and tap on Speech Language to display the list of languages that are installed or else can be installed.

3. Select your preferred speech language that you want to install and tap on it. Tap Yes to start downloading.

4. Once the language pack is downloaded, you are notified that Your update is ready to be installed. Tap install and the phone will automatically restart.

5. Wait for your phone to install the update, during that you will see gears rotating on the screen for up to 5 minutes. 

6. Once ready, a new screen stating that the update is completed. Tap done and the start screen are shown.  

7. You can access voice commands by pressing and holding the Start or Search key (depending on which Lumia update you have).