Other's instructions seem a bit ambiguous. Let me make it as clear as possible with step by step instructions: 

TO ADD ANOTHER PARTNER

1. Open the Schedule K-1 Worksheet(Press F6 and Type in K1W and press enter). The worksheet does not show on the "forms in use" menu that normally  appears to the left of the return you are working on
2. Click on any of the fields for the existing partner (like the ID # or Name)
3. Press the Page Down key on your keyboard.
4. A new worksheet will appear and you can enter the next partner's information.