@shallow-blue saidIt can be a bit tricky.
There's a button "Profile Images" just underneath the bar with your name in it.
You have to get the size more or less exactly right
@mwmiller saidIt is currently not possible from the apps. (Android/iOS)
It's not difficult from a computer, but you do need to pay attention to the image size to get it right.
Can it be done with an app? I rarely use a phone here, but in looking now I don't even see an option to add images to your profile from the app. (iphone)