Ubuntu -- Change the default program used to open a type of file

Run Nautilus, right click one of those files, choose "Properties" from the context menu and set your preferences with the "Open with" option.

"You can use the Properties tab on a file to change the program used to open it, as Manni pointed out.

Edit: Have a look at Chris089's answer. I'd prefer that to directly editing the files as I suggested below. It might still be useful to know what the mime-types are and where the associations lie, but I'd use the tool to modify the file.

However, if you want a text-based solution, or even to have a look at how file-associations are configured for different types:

The file associations are stored for each individual user in ~/.local/share/applications/default.list. You can edit this to point to a .desktop file (which represents the executable)

$ cat ~/.local/share/applications/defaults.list
[Default Applications]
application/vnd.google-earth.kml+xml=Google-googleearth.desktop
application/keyhole=Google-googleearth.desktop
application/earthviewer=Google-googleearth.desktop
application/vnd.google-earth.kmz=Google-googleearth.desktop

At the global system-wide level, associations are held in /usr/share/applications/defaults.list. So, if I wanted to effect a system-wide change for all audio files for example, this is where I'd need to look to get all the mime-types. You then have a choice between changing the file types directly here, or overriding them in your local defaults.list

$ cat
/usr/share/applications/defaults.list
| grep ^audio
audio/3gpp=totem.desktop
audio/ac3=totem.desktop
audio/AMR=totem.desktop
audio/AMR-WB=totem.desktop
audio/basic=totem.desktop
audio/midi=totem.desktop
audio/mp4=totem.desktop
audio/mpeg=totem.desktop
audio/mpegurl=totem.desktop
audio/ogg=totem.desktop
audio/prs.sid=totem.desktop
audio/vnd.rn-realaudio=totem.desktop
audio/x-ape=totem.desktop
audio/x-flac=totem.desktop
audio/x-gsm=totem.desktop
audio/x-it=totem.desktop
audio/x-m4a=totem.desktop
audio/x-matroska=totem.desktop
audio/x-mod=totem.desktop
audio/x-mp3=totem.desktop
audio/x-mpeg=totem.desktop
audio/x-mpegurl=totem.desktop
audio/x-ms-asf=totem.desktop
audio/x-ms-asx=totem.desktop
audio/x-ms-wax=totem.desktop
audio/x-ms-wma=totem.desktop
audio/x-musepack=totem.desktop
audio/x-pn-aiff=totem.desktop
audio/x-pn-au=totem.desktop
audio/x-pn-realaudio=totem.desktop
audio/x-pn-realaudio-plugin=totem.desktop
audio/x-pn-wav=totem.desktop
audio/x-pn-windows-acm=totem.desktop
audio/x-realaudio=totem.desktop
audio/x-real-audio=totem.desktop
audio/x-sbc=totem.desktop
audio/x-scpls=totem.desktop
audio/x-speex=totem.desktop
audio/x-tta=totem.desktop
audio/x-wav=totem.desktop
audio/x-wavpack=totem.desktop
audio/x-vorbis=totem.desktop
audio/x-vorbis+ogg=totem.desktop
audio/x-xm=totem.desktop

Here is the Desktop Entry Specification document that details the need for and use of a .desktop file (instead of using the path to the executable )."