alter tablespace

I was trying to change the settings for a temp tablespace attempting to increase the size of its next extent through this command:
ALTER DATABASE DATAFILE /DATAFILE NAME/ AUTOEXTEND ON NEXT 10M.
I've got a prompt saying database altered.
When I queried next_extent from dba_tablespaces for my tablespace it was still showing old value.
What am I missing? I couldn't find other command which will increase the next extent value.

It will show you the new value only it is allocated with the new data. If you want see the size then look into the DBA_DATA_FILES view, then you should find the increased the size