If you are using the forked version of freepbx, just do on the trixbox SSH:
yum remove trixbox
yum remove tbm-pbxconfig
Then "upgrade" freepbx by using these instructions:
Then, update all the modules with Module Admin and Check for Updates online
While you are doing that, install the Backup/Restore module
Backup your current data. Use winSCP to get into the trixbox to grab the backup file. It is located at /var/lib/asterisk/backups
Get on Elastix and get on the non-embedded freepbx. Install the backup/restore module. Make a backup of what you have (only to create the "backups" folder.) Then use winSCP to place the backed up file in /var/lib/asterisk/backups and in Freepbx, click on the Tools tab and click backup/restore. Click to restore a backup and you will see your file there. Restore the entire backup set.