What version 6 release? You need to be at 6.0UR3 to use the Migration utility to do the VXWorks to uBoot migration. Go to edocs.mitel.com and find the Migration Guidelines doc for MiVB release 9.4, make sure you understand that before continuing. You'll need to run an audit on the 6.0 system to ensure that migration is possible without making some changes/corrections to system programming, then run the migration tool to actually upgrade the AX firmware to support the o/s switch.