Cannot choose WordPress template when activiting forum

Ok, I have full forum features activated with Muut plugin and set Enable forum in page edit view. But when I enable forum I cannot choose WordPress template for the page. The problem is that I have still wordpress sidebar in my forum page, when I actually want to get rid of that and use Muut sidebar instead. Muut forum and sidebar shows up great, but wordpress sidebar is dropped below Muut and that is looking very bad. How to get rid of WordPress sidebar in forum page?

My forum is here:
http://digiapuri.com/keskustelut/

https://wordpress.org/plugins/muut/