If you’re over level 20 and unhappy with your build, most players recommend you just start over again. Path of Exile doesn’t allow you to fully reset your Passive Skill Tree.
And if you’ve made a mistake in your build, there are only a few ways to repair it. There are over 1200 nodes to choose from, and you will need to use all the skill points you earn while leveling up to reach the distant, powerful nodes. The Path of Exile Passive Skill Tree is daunting.