If you are moving all of the Topics in a Board to one specific Board:
Go to Admin>Boards>Modify the Board and click to Remove it.
You should get a notice that will allow you to choose which Board to move them to.
If you are moving Topics in a Board to several different Boards:
First go to your Profile > Look and Layout Pref - set this to "checkboxs" - "Show quick-moderation on message index as"
Go into the Board that you want to move the Topics from.
Put checkmarks across from the Topics you want to move.
Go to the bottom of the page
Use the left dropdown box - choose "Move Selected To"
Use the right dropdown box to choose the Board you want to move them to.
You'll have to keep doing this until you get them all out of there.
Note: if you have a LOT of Topics in that Board go to Admin > Posts & Topics > Topic Settings - up the number of topics to show on the page so you can get thru it quicker