The MODIFY clause

Use the ALTER FRAGMENT statement with the MODIFY clause to modify one or more of the expressions in an existing fragmentation strategy.

Suppose that you initially create the following fragmented table: 
CREATE TABLE account (acc_num INT, ...)
   FRAGMENT BY EXPRESSION
      acc_num <= 1120 IN dbspace1,
      acc_num > 1120 AND acc_num < 2000 IN dbspace2,
      REMAINDER IN dbspace3;
When you execute the following ALTER FRAGMENT statement, you ensure that no account numbers with a value less than or equal to zero are stored in the fragment that dbspace1 contains: 
ALTER FRAGMENT ON TABLE account
   MODIFY dbspace1 TO acc_num > 0 AND acc_num <=1120;

You cannot use the MODIFY clause to alter the number of fragments that your distribution scheme contains. Use the INIT or ADD clause of ALTER FRAGMENT instead.