I'm basically modifying Top Discussion This Week page using Text Editor.
How to modify then?
Be sure to change "Top Discussions this Week" heading to "Discussion Forums" via Language Editor ( search "Top Discussions" in search field.)
Be sure to check "Top Discussion" and "Display leaderboards for the last week" from the Leaderboards Settings.
If you have some knowledge of HTML and photoshop, go to this page http://www.yournetwork.com/leaderboards/discussions/week and customize it using Text Editor.
Go to "Tabs and pages" via my network and change the Target page i.e. http://www.yournetwork.com/leaderboards/discussions/week
If you don't have any idea how to do this-you may contact me @ email@example.com