Step 1 - Go to Catalog

Click on the catalog icon in the top left of your app.

Step 2 - Select My Boards

Press on My Boards in the top navigation bar to find the board you want to delete from the catalog.

Step 3 - Press and hold to delete boards

Now press on the item you want to delete and keep pressing until you see a "X" icon appear to delete the item.  It works the same way as deleting apps from your device.