**1.**
Please take a look at [this][1] Stack question. It points to a [tutorial blog][2] on how to do this.

In SPD open `default.master`, then add the script:

    $(document).ready(function()
        {
        var form = $('form');
        if ( form.attr('action').indexOf('YOUR 36 character List ID - Without Braces') > -1 )
            {
            var checkbox = $('#ctl00_PlaceHolderMain_UploadDocumentSection_ctl03_OverwriteSingle');
            checkbox.removeAttr('checked');
            checkbox.parent().hide();
            var multiple = $('#ctl00_PlaceHolderMain_UploadDocumentSection_ctl03_UploadMultipleLink');
            multiple.hide();
            }
        }
    );
**2.**
 There is another question on Stack [here][3], where Falak Mahmood suggests that manually changing the Upload.aspx in 12/14 hive is not recommended. Instead, he suggests:

> ...to write a custom Feature which has AdditionalPageHead delegate
> control to un-check the "Overwrite existing file" (using jQuery)
> option while uploading the documents.


  [1]: http://sharepoint.stackexchange.com/q/75382/16290
  [2]: http://sharepoint4u.wordpress.com/2013/08/13/how-to-disable-overwrite-exisintg-files-in-a-library/
  [3]: http://sharepoint.stackexchange.com/a/47783/16290