I spent a while figuring this out (to set up a problem/resolution scenario for ITCAM) and figured I would share.
By default, DB2 has auto-commit turned ON. So any time you run a SQL statement, it's automatically followed by a COMMIT. To change this, the easy way is:
db2 +c "delete from your_table_name where your_where_clause"
Then any other application or process trying to read or write this table will have to wait until the lock is cleared before returning. So if you open another window and run 'db2 select * from your_table_name', it will just sit there.
To clear the lock, run:
More info is here: