Below is some SQL that can be used to rename a column by dropping the column and adding the new column name.  Do realize that this will make you lose the data in the OLDCOLUMNNAME field so you’ll want to create a backup and re-populate the new field using the backup.

Create backup
CREATE TABLE MYLIB.MYTABLEBACKUP
AS (SELECT * FROM MYLIB.MYTABLE)
WITH DATA;
::WARN:: This will tell the server to drop columns even if there is data in the column
CALL QSYS2.QCMDEXC('ADDRPYLE SEQNBR(1500) MSGID(CPA32B2) RPY(''I'')');
CALL QSYS2.QCMDEXC('CHGJOB INQMSGRPY(*SYSRPYL)');
Alter table, drop column and add column
ALTER TABLE MYLIB.MYTABLE DROP COLUMN OLDCOLUMNNAME ;
ALTER TABLE MYLIB.MYTABLE ADD COLUMN NEWCOLUMNNAME CHARACTER (1) ;
Pull the data back in

Note: If you get Error code -952, SQL state 57014: [SQL0952] Processing of the SQL statement ended. Reason code 10. Its because the ALTER TABLE will result in data loss. The database is trying to warn you and wants you to confirm deletion but jdbc can’t handle the prompt. I’m unsure if there is a JDBC option to always say yes to the prompt. You may have to run this in a 5250 session with STRSQL

Alternatively you could also use the command below
CHGPF FILE(MYLIB/MYTABLE) SRCFILE(QDDSSRC)

You would just need to create the DDS in the source file member MYTABLE that changes the column