Have you tried right-clicking the files and selecting Preview in Windows Explorer?
IrfanView will allow you to view most image formats, including JPEG2000. You might need to do a custom install rather than a default one to select which formats are associated with IrfanView, otherwise it will become the default program for all your images.
Photoshop, Paint Shop Pro and most other image editors will also allow you to edit them if required.
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