Change in column settings not working

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SharePoint

I have a column that I created for a library, which I made a site column before adding it to the library page. When I created the column I made it a required column to ensure the column had a value in it. I now would like to change this column to no longer be required and am having some trouble. I have changed the column settings from the library settings page (clicking library settings then selecting the appropriate column) and also the settings of the site column (selecting site settings, then site columns and then the appropriate column, but when I create a new document the document will not save without entering a value in the column that I have now made a not required column.

Any suggestions?

Thanks Kate.