You should be able to change your picture by following these steps:
[1] Hover over your profile/name on the right corner of the forums. After doing this, you will get a drop-down menu that looks like this.
> http://prntscr.com/m1vkyf
[3] From this point on, you will get a small box giving you two options to upload a picture. One is manually straight from your desktop or computer, while the other is through Gravatar. From my experience, Gravatar uploads the image much quicker than uploading it straight from your desktop.
If you upload from your desktop, be sure that the image is 200x200 pixels.
If you want to upload from Gravatar, create an account if you haven't already and link the email you used to create the account.
To create an account for Gravatar, click on the "What is Gravatar" option on the bottom.
> https://prnt.sc/m1vktl
If you still have issues uploading an image, contact me privately and I can assist you from there.