Why and how do councils and academies sell off school land

Of course academies can't sell off land, say the ministers, it's only on lease to the academies, it's held by the councils...

...this is how it's done, according to someone who has just written on my Facebook feed:

"Our local secondary school (in Surrey) had no choice but to become an academy and sell off playing fields to rebuild the school. The school was falling down around them and no/not enough money coming in from council/government to help them have a school that was habitable for students. Sad it had to come to that."