1. Launch the program GeoViewer (a free download from www.lizardtech.com).
2. Go to File > Add Layer > Local Layer to bring in the image.
3. Once the image appears, go to Layer > View Layer Metadata.
4. Look under "Image properties". In the value for Format, a generation 4 MrSID will show MRSID/MG4RASTER.
3. Tools > Export > Export Map