Since you have customized design we might have some problems helping you.
You can use Builder to remove your left column.
If you sign in as Admin to your forum you should see a tool bar above your website.
On the tool bar you should see Builder click on it then click Enable Builder.
After that you should see on the left side of your forum the red crosses, click on them to delete all of the blocks on your left side of the forum.
After you deleted them all click on Builder again and click Save Changes.
See if that did the trick.
If you still have that column on the right side then I will need to go to Control Panel> Customize design > Forum > General appearance of forum pages
And remove $GLOBAL_CLEFTER$
Use F3 if you can't find it.
Save it and your done.
If you still see the column then we need to see your code that is located at
Control Panel> Customize design > Forum > General appearance of forum pages