Running FreePBX 13 and Asterisk 11.
Can I use the updater script to FPBX 14 like that or do I need to upgrade to Asterisk 13 first?
FreePBX 14 still supports Ast 11, so there should not be a need to upgrade. Get a solid backup before running the upgrade script, there are a few reports of major issues. The upgrade script is still an early beta.