how to change preference of application used to open a file?

i accidentally set my preference to always open files with Adobe Acrobat. I am trying to open a file with a different application. then I tried deleting Adobe Acrobat to fix the problem. Now I get this error message:
cannot open or execute file
System Error. Code: -2147221003.
Application not found

What preferences? WinSCP preferences? Or Windows file association? Can you post some screenshots documenting your settings?