Well you may need to ask your host if mogrify is installed on the server. If it is in Admin => Edit Config you would place the proper path to mogrify on the server usually
/usr/bin/mogrify
or
/usr/local/bin/mogrify
If your server does not have mogrify try setting your image processor to GD2 in global options in admin and try uploading then. If you need further assistance let me know.