Instructions
Zoom into your "Zoo Tycoon" game by clicking on the plus sign. Get close enough to easily see the guests in your zoo.
Review the cheats that you can enable by renaming guests (see Resources for list). Each different guest name will cause something different to happen in your park.
Click your left mouse button on a guest in your park. A small box will pop up with the selected guest's information inside.
Double click your mouse in the top of the dialog box where the guest's name is located. Type in the new name you have chosen for your guest. Hit the "Enter" key on your keyboard to save the name. Click the "X" in the top right corner of the dialog box to exit.