VLC Media Player (a free media player that plays many different formats of media files) will also play .iso files.
Freemake Video Converter is a good simple to use (and free) media converter to get started with - I use it to copy and convert the larger .mkv files to smaller .mp4 files (so something like Harmy’s ROTJ 20gb .mkv file becomes a 3gb .mp4 file.
As other people have said there are other software out there too like Ripbot264, Handbrake, Vidcoder, MeGui, etc…