How to decrease temp tablespace in oracle?

Answer 1

Do you want to know how to actually code the commands or the steps required?

To change the size, close the database, change the size of the temp table space and restart. The temp tablespace is used for sorts and result sets, so when the db is closed it is empty and can be manipulated. If you cannot close the db, create a second temp tablespace of the required size, make that the default and then drop the original tablespace.

If you want the commands to do this, refer to the Oracle documentation on create, alter and drop tablespaces.