First select a configuration file from the right hand side navigation (e.g. FEATURES). The file will open in big text box from where it can be modified. Once the file is changed, click on 'Save' button.

If there is a message saying 'Configuration files not updated' visible, click on 'Import current file' or 'Import All Files' button to update the files. This error usually happens if configuration file is changed through system console (shell).

NOTE: Once any kind of file update is done be sure to Reload PBXware to apply the changes.