max size on autoextensible datafile.

 I haven't really worked much with autoextensible datafile. But for the new application requirement, I created a datafile with autoextend on and set the max size to 40G. My question is , if later the datafile is extended to its max size, is there a way I can modify the max size to a bigger size say 50G, or is adding another datafile be my only option? My version is 10.2.0.3. Thanks.