Hi!
You can achieve this with a relatively small amount of css:
.bbpress #sidebar { display:none; }
.bbpress #left-div { width: 100%; }
You will need to create a new image for your background though as it is currently not long enough, then you can add a little more CSS for that too.
Good luck!
Could I get a little more explanation possibly? I am using an elegant themes theme, so I do not if I can edit it’s CSS and get the same results. Also what do you mean by it’s not long enough?
I appreciate it!
Also where to put the code haha.
Your background image doesn’t stretch full width, so you would have to look at either making it longer, or removing it and just have a solid colour.
The code can either go inside your style.css or if you want to do it properly you can follow the instructions here: https://codex.bbpress.org/theme-compatibility/ and then edit the files inside /css/ in your theme files.