Depends on why it is read-only.
The simplest suggestion is to right-click the icon for your file in Windows
Explorer, select "Properties", then uncheck the "read-only" flag.
If this is related to User-Level Security, then sign on as a user that has
full access.
If this is an MDE file instead of an MDW, then get the MDW file and revise
that, then create a new MDE for distribution.
If you are running this file off of a CD or other "read-only" source, then
copy it to a writable source (hard drive), remove the read-only flag, then
open the file from there.