Hi Adam, thanks for your question. It really depends on your WordPress theme. I use here Storefront from Woothemes and to achieve this, to have forum across the whole page, I had to customize additional CSS file.
I have added following code:
In plain English, In all forum pages, I have hidden the sidebar and increased the width of the main area to 100%.
You can try to copy this code to the additional CSS file of your WordPress theme. Majority of themes this day have got an area where you can add additional CSS code. It is usually available after clicking Customize button at the top of the page (you need to be logged on).
If you struggle, let me know what theme you are using and I will try to check how to sort this out.
This reply was modified 1 year, 9 months ago by Pawel.