Hedge help

Hi

I have a hedge all around my garden, not sure what it is as i am new to gardening. The top 1/4 has got leaves but you can see though them and the rest 3/4 is just branches. Some of it has got ivy growing in it. So the garden is not private at all. How can i get it so all of the hedge has thick leaves and nice and private.

Thankyou for your time
Ryan