Question: I wanna change the color of an image in Illustrator. I've downloaded one flat icon from google in png format I just wanna change the color of that particular icon. Kindly help me with the same.

Answer: 
PNG is a *raster* format.

Illustrator is a *vector* editor, that wouldn't be possible, here are some possible workarounds:

If it's a single color icon you can easily change the color using Photoshop.

If it's simple enough, you can trace it in Illustrator and turn it into vector paths which would be usable in Ai.

I would recommend trying to get a vector format of the icon. 

Some common vector formats are `.ai`, `.eps`, `.svg`
To be clear, Welz is ***totally*** *correct* that altering a placed raster image in illustrator isn't the best or most effective workflow at all, and should in most cases be avoided.

---

That said, it depends on the image / logo you have whether you can 'alter the colour' in Illustrator... but there is a 'trick' you can play which will allow *easy shifting of the **overall hue*** of a placed image, which functions like colourising the whole image; it's *not* subtle, it's a blunt-instrument approach, but it can work well for some specific use-cases.

It will do ***nothing*** if the *primary* colour in the placed image is **black**.

---

Add a rectangle above your placed image, fill the rectangle with colour, and set its opacity / blend mode to colour, then alter its colour as desired to get the effect you wish.

Base colour of placed image:
[![enter image description here](https://i.stack.imgur.com/c7zLA.png)](https://i.stack.imgur.com/c7zLA.png)

Rectangle above with hue shifting to yellow-orange:
[![enter image description here](https://i.stack.imgur.com/7QYpz.png)](https://i.stack.imgur.com/7QYpz.png) 

Rectangle above shifted to green:
[![enter image description here](https://i.stack.imgur.com/bgePq.png)](https://i.stack.imgur.com/bgePq.png)

---

If either your placed icon is black, or you wish more control, then everything Welz has said is spot-on: use a raster image editor for raster image work, vector for vector - far more effective and efficient, and better match of tools for needs.

Hope this helps.