I’ve let the conifers at the bottom of my garden grow far too tall, need to ‘top’ them, is it as straight forward as cutting to a desired height or is there a specific way of doing it so I wont actually kill them or turn them all brown (I’ve been told this happens)

Depends how tall they are, you might want to tie them up, but basically just lop the tops off.

How high are they and how close together?
If they are close (i.e. a hedge) you may find that the branches are intertwined and it will be very hard work pulling them down.

Also, how are you going to cut the trunks? Saw, chainsaw? Be careful.

I’d give serious consideration to cutting them down completely and replacing with something nice such as a beech hedge.

I’ve cut ours three or four times with a bow saw. The trunks and branches are easy to cut through and it leaves a more natural look than a chainsaw cut. One of the trees has gone patchy brown but the others are ok.

If by conifers you mean Lleylandi then just lop them. You won’t kill them. Where you need to watch is if you cut them back from the side. If you go past the green then they might not grow back.

In inherited a Lleylandi hedge down one side of my garden. Only 8 feet high but on the sunny side of the garden so blocking a lot of light. Also extending 4 or 5 feet into a not too big garden.

The best thing I’ve done to my garden was digging that hedge out and replacing it with wooden fencing.

As for technique. I found loppers and a handsaw from the top of a ladder were fine. No need for power tools.

If you are ever removing them don’t cut the trunks below about 6 feet until the roots are out. The leverage helps when rocking them to get at the roots.

If I was planting a hedge from scratch I’d agree with Beech. Not too fast growing. Can be kept narrow if you wish. Can be cut back hard and re-grows. Nicer to look at.

I’d give serious consideration to cutting them down completely and replacing with something nice such as a beech hedge.

That’s what we did. Leylandii was up to 5m thick, 4m tall. No coming back from that!

If I was planting a hedge from scratch I’d agree with Beech. Not too fast growing. Can be kept narrow if you wish. Can be cut back hard and re-grows. Nicer to look at.

Or Hornbeam. Pretty similar, but does better in wetter/clayier soils. Leaves don’t stay non quite as well during the winter, but leaves come out 3-4 weeks earlier in spring.

After you’ve topped them are they going under the patio or into the decking?

As has been said, they’re easy to top, best place to start is at the bottom.

Topping is straightforward enough, might not be that aesthetic a result for a couple of years but should normally grow back to hide the cut (may vary with species I suppose). If you’ve got a lot to take off just do it a bit at a time for safety, you don’t want half a tree falling on your head when you’re up a ladder. Consider cutting a bit lower than you want so you’ve got some years in hand before they get too tall again!