Você vai querer navegar para Control Panel\All Control Panel Items\Default Programs\Set Associations dentro de uma janela do Windows Explorer para alterar a associação de extensão de arquivo para o programa de sua escolha.
Open Default Programs by clicking the Start button Picture of the Start button, and then clicking Default Programs.
Associate a file type with a program
Use this option to fine-tune default programs based on the file type or protocol. For example, you can have all .jpg image files open using a specific program, and .bmp image files open using a different program.
Set default programs for this computer
Set Program Access and Computer Defaults (available in Windows 7) is a tool to set default programs for activities such as browsing the web and sending e‑mail for everyone who uses the computer. For more information, go to the Windows website and search for "Set Program Access and Computer Defaults."