Instructions
Double-click on the "Roblox Studio" icon on your computer desktop -- or wherever you have it on your computer -- to launch the application.
Select the "Models" option then click on "Humanoid." You will see your Roblox humanoid on the main stage of the application.
Click on the head of your humanoid character. The settings for the head will appear in the side menu. Set the "Transparency" for the head to "1." This will hide the head and head script as well. You can then create a new head from the "Models" menu and attach it to the humanoid body by clicking on the "Weld" option in the top menu.