Option 1:

The GDAL libraries can accomplish this. They are installed with QGIS, for example, but can also be installed and executed without any GUI from the command line. You basically need to enter two things: The output format (-of: GeoTiff is GTiff) and the target coordinate system (-t_srs: WGS854 is EPSG:4326). If the GDAL binaries are included in your system's path variable you can just call them from the command line. In your case it would be:

gdalwarp -t_srs EPSG:4326 -of GTiff input.h5 output.tif

where input.h5 is the file you want to convert and output.tif stands for the result. This line makes a GeoTiff in WGS84 out of your H5 product.

Note that if your H5 file consists of many layers you have to address them by their name according to the following standards: HDF5:file_name:subdataset (documented here: http://www.gdal.org/frmt_hdf5.html)

Option 2:

There is also an online converter for this but I haven't tested it and I don't know if it is reliable or restricted regarding file size:

https://mygeodata.cloud/converter/hdf5-to-geotiff

https://trac.osgeo.org/gdal/wiki/DownloadingGdalBinaries

http://www.gdal.org/gdalwarp.html

http://land.copernicus.eu/global/faq/how-convert-swi-hdf5-data-geotiff