On a computer (using Chrome):
Click on your name in the upper right hand corner:
Now click either the second version of your name or "account details":
If you clicked your name here is where you will be:
Now move the cursor over the current picture and click edit:
Here is where you will be when you do that, now just click choose file:
If you clicked "account details" here is where you will be, just click it to get to the choose file part:
And you will be here this way also, just click choose file:
Then you will be able to move it around and then hit "Okay"
There you are, for Chrome on a computer! Good luck.