You can find out which files are linked via this command

DSPDBR FILE(LIBRARY/FILE_NAME)

And in spool file you can find results

Files Dependent On Specified File                                     
  Dependent File         Library       Dependency   JREF    Constraint
      FILE_1             LIBRARY1      Data            1              
      FILE_2             LIBRARY2      Data            1              

Then you can try first to delete member with same name in joined logical files

You will need information about Volume serial and Sequence from BRMS

Code 4 -- Journal sequence number is at the maximum value.

Means that Sequence number is on maximum level (this is screenshot from MIMIX) :

Best way to generate key pair is to use ssh-keygen utility: 
ssh-keygen -t rsa -b 4096 
ssh-keygen -t dsa 
ssh-keygen -t ecdsa -b 521 
ssh-keygen -t ed25519 

You can also check actual settings on other files in your libraries.

First run this SQL to collect information about object sizes in all user libraries on your system.

CREATE TABLE YourLibrary.FileName AS (SELECT OBJNAME, OBJLIB,
OBJTYPE, OBJCREATED, OBJSIZE FROM TABLE                    
(QSYS2.OBJECT_STATISTICS('*ALLUSR','*ALL')) X ) WITH DATA  

After this step you can list all files with *MAX4GB ordered by file size.