The Launch button is wired up to look for the current version of Visual Studio in the Registry, so if you find that an older version gets launched, its because you have either installed the older version after the latest version, or reinstalled it or did something else that will have changed the current version of VS. You just need to change the current version back to the most recent release. Since this involves making changes to the Registry, the usual sensible advice applies - make a backup of your registry beforehand .
Type Regedit in Search Programs and Files in your Start menu, double click regedit.exe and select the HKEY_CLASSES_ROOT branch. Navigate to VisualStudio.DTE. Change CurVer to VisualStudio.DTE.10.0 for 2010, VisualStudio.DTE.11.0 for 2012 or VisualStudio.DTE.12.0 for 2013. Then change CLSID to {656D8328-93F5-41a7-A48C-B42858161F25} for 2010, {059618E6-4639-4D1A-A248-1384E368D5C3} for 2012 or {3C0D7ACB-790B-4437-8DD2-815CA17C474D} for 2013. You can copy this value from here, or by opening the relevant CLSID node in the registry (which should be just below where you are working) and copying it from there, once you have double clicked "Default" in the editor to invoke the Edit Value box
Job done. Now the right version of VS should fire up at the click of that button.
If you found that it all went horribly wrong and nothing works on your machine anymore, I hope you backed up your registry...
