Read-only Excel file

I am using Excel for Mac 2011, Version 14.2.5. I have a workbook open, and in the Atributes the Read-only box is checked and is grayed out. How can I change this so Read-only is not checked? I have tried saving-as, changing the name, deleting the original file, and then renaming with the file name I want. As soon as the file is named the same as the original file I get the "the file is locked by another user (me!), would you like to open a read-only copy?"