Hi and welcome!
Your profile picture and avatar pictures are actually two separate fields on your profile.
You can use the same picture for both if you'd like. Here are the instructions for updating your avatar. After you do it, wait about 10 minutes and then you'll see it show up on your posts - even ones before you did the update
Please let me know if I can help you with anything at Splitcoast!
Splitcoaststampers - Help