Try this to upgrade to 2.16 is in my network and is working.
1. Invoke the IVR by going offhook on the analog touchtone phone connected to port 0.
2. Press the button on the top of the ATA 186.
3. Key in the following on the touchtone phone to instruct the ATA to download software. 100#209*227*165*146*8000#
4. Remain off hook while the ATA attempts to load the new software. The IVR will inform you whether the upgrade was successful or not.
5. Once the IVR reports on the success of the upgrade, hang up the phone.