Use this tutorial :
Default File Associations - Restore in Windows 8
http://www.eightforums.com/tutorials/8486-default-file-associations-restore-windows-8-a.html
1.Scroll down to the table and select .....
.exe
2.Save the 
.reg file to your desktop.
3.Double click or right click 
.reg file > select  
Merge 
4.If prompted, click/tap on 
Run, 
Yes (UAC), 
Yes, and 
OK to approve the merge.
5.Restart computer to complete the process.