Tutorial - How to create a world using Real-World Height data

Hmmmm....I did everything perfectly, except I get two maps instead of one. I know this is because the map isn't in 16 bit. I'm using paintshop pro, and when I try to save the image it comes up with this message: "because of the requirements of the specified file format, the saved file will have a bit depth of 24 (16.7 million colors). Would you like to continue?". Obviously, I don't want thi. However, I don't know how to fix the issue, so I CAN have 16 bit. Sad face. What do you recommend?