The forum has a default theme (style) and one other theme which can be changed by selecting it in user control panel settings. These diagrams should help you change those settings.
Follow the same steps as above, but instead select Avatar as per the diagram. You can also choose a Gravatar which is an image linked to whichever social media account you selected a gravatar for in the first place, IE Google+ or a blog for example. Avatars are not mandatory, but are a useful way to identify members.
The control panel allows you to change other settings which include:
Signature - some text and/or an image that appears at the end of your post.
Privacy - who can see you.
...change username and password along with several other settings which are self explanatory.
Remember to hit SUBMIT once you've made the changes.
Some options shown in the diagrams may only be available to administrators.