Purchase and download Muscle Premium for your platform (either Mac or PC) at http://www.visiblebody.com/products
Locate and launch the installer to begin installation. The file name is "Muscle_Premium_Installer.dmg" on Macs, "Muscle_Premium_Installer.exe" on PCs.
Follow the on-screen instructions to install the application onto your hard drive.
Open the application and enter your serial number to activate Muscle Premium.