Reduce size or recreate undo tablespace

Hi,

I notice that my UNDO datafile has grown from 200MB to 1GB. I tried to reduce the size but it doesn't allow. How can I strink the file back to 200MB or drop and recreate back? I'm not allow to offline the tablespace and thus cannot delete.

To recreate:

1. Create a new undo tablespace
2. Change the 'undo_tablespace' parameter to the new tablespace name.
3. Drop the old tablespace (obviously you will have to have no active transactions in this tablespace before you can do this)

jovery,

For no.2, how to change the 'undo_tablespace' parameter to new tablespace? Tks.

Alter system set undo_tablespace = new undo_tablespace