If you need to override the default max file sizes, you'll have to open the file that the RAD editor is being used on (for example topic.aspx, entityEditProducts.aspx, etc) and find this line:
Code:
<tcontrol:RadEditor runat="server" RadControlsDir="rad" id="radDescription">
....and add the desired 'MaxUploadFileSize' attribute(s). There are 3 - DocumentManager-MaxUploadFileSize, MediaManager-MaxUploadFileSize, and ImageManager-MaxUploadFileSize:
Code:
<tcontrol:RadEditor runat="server" DocumentManager-MaxUploadFileSize="512000" MediaManager-MaxUploadFileSize="512000" ImageManager-MaxUploadFileSize="512000" RadControlsDir="rad" id="radDescription">