But my advice is, think twice, and think again, before updating Mapsource beyond v6.13.
And if you already have v6.14 or higher, you may want to consider downgrading.

v6.137 is still available from Garmin's website here: http://www8.garmin.com/software/MapSource_6137.exe the download is around 45Mb in size.
(In case Garmin withdraw this file, it can also be found at gpsinformation.org here - 6.137.)
Simply download the .exe file and run it, to 'update' your version of Mapsource. If you like, you can view Garmin's own instructions for updating Mapsource here.

I think it's a good idea to backup your Mapsource directory first - just the program files, not the maps which can be huge and won't be affected by this. The default install directory is C:\Garmin but of course you may have installed it elsewhere - I know I did!
Or set a System Restore point.

You can have both versions.
I quite like the new version for its improved map render - especially if I wanted to print out a bit of map - but generally I find it too slow - so I have both old and new versions co-existing like this:
Before updating or downgrading:
* Navigate to the folder where Mapsource is installed.
* Make a copy of the existing file Mapsource.exe into another folder (eg /temp/ ).    (As confirmation, this file is approximately 10Mb)
* Navigate to the copy, and rename it, say, with its version number eg Mapsource614.exe.
* Navigate to the new version updater that you've downloaded, and run it, to update or downgrade Mapsource.
* Try it out.
* Navigate to Mapsource614.exe and move or copy it back into the Mapsource folder.
* Create a new shortcut for Mapsource614.exe.
* You can now simply run either version, pre- or post- update - and whichever you run 'remembers' your last settings so you can switch between two views of the same area, as I did for the screenshots above.