1.If you would like to save changes to a read-only file you will need to unlock it first. Click the Save button 
and the Save Map dialog box will appear.
There will be a closed lock 
before the map file's name.
2.Select the file's name and click the unlock button 
in the top right hand corner of the dialog box.
This will unlock the file enabling you to save any changes to the maps. See To save an existing file.