Hello There, It depends on the size of your tree. It is a small tree you can do it by yourself all you need to buy is a big scissor for cutting leaves and small branches. But if the tree is big and tall that's the time you will call a Tree Trimmer Service. You can go to the web and search for the nearest service in your location.
Here ill show you the actual trimming of tree in my backyard
This is what I'm trying to say to you if your tree is tall it is dangerous for you to climb up. That's, why you need to call a service, will help you to avoid accidents.