First remember that your Me profile picture will be shown on other users caller id,
and also in your public Me profile, moreover it can be saved as a contact on your friends contact list with our Me Picture sync feature, so choose something nice 🙂

Now, in order to change your profile picture go to Profile Tab -> Tap on Edit
Then just tap on your profile picture
(you will need to grant the app access to your gallery or media)
choose your desired picture from your gallery -> Tap Done and you are all set!
In order to remove your profile picture go to Profile Tab -> Tap on Edit -> Tap on profile picture and “Remove” this will do the job.