Answer by Thirumalesh.L for How do you remove a default program association for file types in Windows 7?

Open a New Text File .txt and save it in desktop by give any name and extension as .exe and close it, open properties of the file which you want to change open with and in general tab click change in open with column click Browse and select your created .exe file and click ok it will change to your new created program and then delete your exe file that's it then when you open your file it will ask for open with.