Configuration files can be changed from PBXware SHELL or from GUI interface:
cd /opt/pbxware/pw/etc/asterisk
nano ./sip.conf
Press 'CTRL + O'
Press 'Enter'
Press 'CTRL + X'
/opt/pbxware/sh/stop
/opt/pbxware/sh/start
Please note, once changes are saved PBXware reload will be performed automatically, however, some changes will require PBXware service restart in order to be applied.