This is what I did:
>db2 alter table C1016781_T1 alter column itemContent set data type blob(2097152)

and I got:
DB21034E The command was processed as an SQL statement because it was not a valid Command Line Processor command. During SQL processing it returned: SQL0104N An unexpected token "blob" was found following "ontent set data type". Expected tokens may include: "GRAPHIC". ...