Some file types (eg - .jpg) can be opened by several different programs - so you can change the program associated with such a file type (at least amongst the programs that can handle it).
Other file types are associated with particular programs (eg - .ppp (Power Point Presentation)) - and there simply is no other program that you can associate it with.
So it all depends on exactly which file type you are talking about.
If you right-click on a data file, you may have an "Open With" in the menu pane that opens - if you have you can then choose what program to open the file with - but make sure you know which progrmas will actually open the file.
misters, in Windows Explorer, click on a file of the type you want to change the association for, the shift + right click. From the drop-down menu, select "Open with". from the list of programs, select the one you want that file type to be associated with. If you want the association to be permanent make sure there is a tick in the "Always use this program etc" box.
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