In this tutorial I am going to show you how to change eyes color in a very simple way. We start with opening up the image we want to change the eyes color.
After that increase the zoom on your image by pressing Ctrl and + at the same time. After that select the Polygonal Lasso Tool (see in the top left corner on the following image) and start selecting around the eyes. When you finish the first eye and you pass on the second one, press Shift to cumulate the selections.
Now go to Image » Adjustments » Color Balance and select the colors you want. This is my result.