You're welcome to upgrade a Kudoboard at anytime! To do so you'll want to follow the instructions below:
1. When on board, click Settings
2. After clicking Settings, a slider will open on the the right
3. Click the blue upgrade link, and you will then be directed to a new page where you can pay to upgrade your board.
Once this new board has been paid for, you will have immediate access to its features. Any changes made to the board previously will be saved.
Note that this upgrade will apply only to this individual board. If you want purchase an ongoing plan with unlimited boards, there is more information on those options here.