If you want members to update their profile picture, don’t tell them to do it. Not many people will listen to you. Just set the default picture to something extremely ugly and/or funny (I prefer a picture of a smiling pig).
If your want members to update their hometown, age or almost anything else in their profile, you just need to set a default that members wont like.
Likewise, if you want members to fill out a bio, create a ridiculous, but funny, story as the default for any new profile created.
I’ve tried ordering members to update their profiles, I’ve tried asking them nicely and I’ve tried offering rewards to members that update their bios. The single most effective approach has been to set funny defaults.
Just make sure you keep the defaults light-hearted. You don’t want to offend newcomers).