1. Your forum is currently in a sub folder called forum on your hosting.
You will have to change that before you can actually change the url. Woltlab seems to be using a sub folder for forum by default
2. You can make forum your landing page
Try this link
My website in now running like this. http://www.domain.com/forum/thread/topic
I need to set it to http://www.domain.com/thread/topic
I don't need article tab. i only need forum
How can I do it
Have a look at this guide... Change directory structure
You will have to change the directorystructures of your Applications.
Thanks all for the support