Change Eyecolor in Photoshop Easy Way

Step 1: Duplicate the background of your eye image

CTRL + J

Step 2: ADD New Layer

Step 3: We will use Brush tool, Select the hard round brush like in the screen shot below

Step 4: Paint the Eye with any color you like.

Step 5: We will use Gaussian blur

GO to filter > blur > gaussian blur

And thats it

You have to make it look neat by erasing the color outside the iris with your soft round brush,

and you are done