Pruning a crab apple tree

Hi,

Thanks in advance for any help.

Forgive me for my ignorance on this, I'm a total beginner, I had a gardener booked to look at the ten year old crab apple tree in my back Garden but obviously he's not coming now and is unlikely to for a long while yet.

My Mum bought and planted it, for my son. It has never been pruned or cut back, its now growing away from the wall it is planted next to, at an angle of 45 degree from the main bough. It produces masses of fruit but its hanging over a big area of my small garden, casting a shadow over the lawn and getting in the way of the boys playing!

Is it ok to prune it at the time of year?

How low down can I cut? Can I cut enough back that I'm able to cut off a large amount of the overhanging branches?

How much could I take off the top?

I have looked at a few videos on youtube, but I'm still a bit unsure about what I'm doing and I don't want to kill it! The gardener who gave it a quick once over said I could cut one of the main branches right back, but I'l too nervous to go ahead

Thanks again for any help and advice!