how high do i prune the fruit trees to ? Growing against a wall...

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I rent a house on a country estate and have a huge wall along one side of the garden. It has fruit trees growing all the way along it which have gone a bit wild. I am tidying them up, should I level them with the top of the wall ? Or let them grow taller ? They are mainly plums. There are some pears, but I am leaving them because they look ok.

[recall]

the wall is about 12 foot high