How can I put an Icon in Template

[Leachim]

Hi there!

I use the Dimension Theme and I like to add our logo in the middle of the Circle in the theme (look at the picture).
The Theme uses Fontsawesome and there was a diamond as Icon. I saw the code in the template:

id="header">
<div class="logo">
<span class="fa-diamond"></span>
</div>

So now I want to change the diamond icon in something else, how can I do it? The fontsawesome-Code does not work or I put it the wrong way, can smb. help me? What I have to do?

Thank you for reading my post :)
and I hope smb. can help me.