When you install MATLAB® on Windows® platforms, the installer sets up associations between certain file types and MathWorks® products. When you double-click one of these files in the Windows Explorer (file manager), Windows executes the open action specified by the file association. If Windows starts MATLAB, then it opens the version of MATLAB associated with that file type.
By default, MATLAB associates the latest installed version to MATLAB file types. If you use the Windows file manager or the Control Panel to associate a MATLAB version to a file type, then that version remains associated with the file type even when you install another MATLAB. If, instead, you always want to use the latest MATLAB version, then you must manually reassociate the type with each new installation of MATLAB. If you want to return to the default behavior, then uninstall every MATLAB that is manually associated to any MATLAB file type. Then reinstall the latest MATLAB release.
Sometimes double-clicking a MATLAB file in the Windows file manager opens a new instance of the version of MATLAB that is already open. To work around this issue, uninstall versions of MATLAB, release R2010a or earlier. Then reinstall MATLAB R2010b or later.
Alternatively, change the security setting on the
file to allow the
Users group to write to the file. For more
information, see https://www.mathworks.com/matlabcentral/answers/93468-why-is-a-new-instance-of-matlab-opened-when-i-double-click-on-a-matlab-file-in-windows-explorer-even.