Right mouse-click the speaker icon that appears in the System Notification Area by the date and time in the lower right hand corner, and choose Playback devices.
You should see a playback device entry for each Bluetooth profile supported by your headset.
If your device is connected, you will be able to left mouse-click the desired profile and then click the Set Default button. Windows will do it's best to use this profile, such as an A2DP profile, but if an application detects the microphone on the headset and engages it, your headset will revert to the headset profile instead. Windows is usually pretty good about switching profiles when necessary.