Hi
Here's a quick guide I put together for members of my CC. Nobody has said if they are using the PC or mobile, this is for PC only.
On your profile page, click appearance, and then upload a photo

This window opens

Clicking browse opens a window where you can navigate to where you have saved the pic you want to use. Find it, click ok and the place where you saved it is shown in the box left of the button. Now click Upload photo.
Your pic should now appear like this

By dragging on the corners or sides you can enlarge or resize the box on the right untill you are happy with the preview left

All good? Click save.
That should now have changed your profile pic.
Cheers!
Rich