The FreePBX Distro has some built in features to allow you to change the Major Asterisk version you are using.
For example the 6.12.65 release track supports Asterisk 1.8, 11, 12 and 13
To change which Major Asterisk release you are using type;
You will then be prompted to pick which Asterisk Version you would like to switch to
Once the switch has been completed you will be informed which Version you are running and that Asterisk is restarting.
FreePBX will then perform a reload and re-write all the configuration files based on the version of Asterisk you switch to.
You can verify the running version of Asterisk at the bash prompt with:
# asterisk -x "core show version" Asterisk 13.9.1 built by mockbuild @ jenkins2.schmoozecom.net on a x86_64 running Linux on 2016-05-13 20:33:39 UTC
If the old Asterisk version is still shown, you can restart with:
The final step is to reload the system dial plan: