Teacher who would like to become a school business manager

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I am a secondary school teacher. I've had 2 dc and don't plan any more, and I have really got to the end of my rope with teaching. For all the reasons that have been discussed many times, I just want to exit in the next two years.
I love, however, being in schools and am interested in becoming a school business manager. My degree is entirely inappropriate (humanities) and I have experience mainly as a teacher, with a short stint in a study abroad centre overseas advising on the UCAS application process.
What would I need to do in terms or retraining or courses to stand a chance of moving into a role like this?