to begin with your block size is to small it should have been 8k when database was created.
But if this is only an isolated case, you can use that UTLCHAIN.SQL script. For PCT_USED, since you have set it to 75, then the most that you can adjust is up to 85-89 since your PCT_FREE is 10. If this table doesn't made much of UPDATES, then you can lower your PCT_FREE to 5.