Issues on upgrading RDS instance from 9.5 to 9.6

Hi,
Not sure if this will work, but have you tried upgrading using the CLI command aws rds modify-db-instance? Perhaps, if you set

 [--option-group-name <value>] set to "default:postgres-9-5-db-styygdzxjcureomoiuv4tcj5ke-upgrade"

it might work?

aws rds modify-db-instance help

modify-db-instance
^^^^^^^^^^^^^^^^^^
Description
***********
Modifies settings for a DB instance. You can change one or more
database configuration parameters by specifying these parameters and
the new values in the request. To learn what modifications you can
make to your DB instance, call "DescribeValidDBInstanceModifications"
before you call "ModifyDBInstance" .

See also: AWS API Documentation

See 'aws help' for descriptions of global parameters.

Synopsis
********
     modify-db-instance
   --db-instance-identifier <value>
   [--allocated-storage <value>]
   [--db-instance-class <value>]
   [--db-subnet-group-name <value>]
   [--db-security-groups <value>]
   [--vpc-security-group-ids <value>]
   [--apply-immediately | --no-apply-immediately]
   [--master-user-password <value>]
   [--db-parameter-group-name <value>]
   [--backup-retention-period <value>]
   [--preferred-backup-window <value>]
   [--preferred-maintenance-window <value>]
   [--multi-az | --no-multi-az]
   [--engine-version <value>]
   [--allow-major-version-upgrade | --no-allow-major-version-upgrade]
   [--auto-minor-version-upgrade | --no-auto-minor-version-upgrade]
   [--license-model <value>]
   [--iops <value>]
   [--option-group-name <value>]
   [--new-db-instance-identifier <value>]
   [--storage-type <value>]
   [--tde-credential-arn <value>]
   [--tde-credential-password <value>]
   [--ca-certificate-identifier <value>]
   [--domain <value>]
   [--copy-tags-to-snapshot | --no-copy-tags-to-snapshot]
   [--monitoring-interval <value>]
   [--db-port-number <value>]
   [--publicly-accessible | --no-publicly-accessible]
   [--monitoring-role-arn <value>]
   [--domain-iam-role-name <value>]
   [--promotion-tier <value>]
   [--enable-iam-database-authentication | --no-enable-iam-database-authentication]
   [--enable-performance-insights | --no-enable-performance-insights]
   [--performance-insights-kms-key-id <value>]
   [--performance-insights-retention-period <value>]
   [--cloudwatch-logs-export-configuration <value>]
   [--processor-features <value>]
   [--use-default-processor-features | --no-use-default-processor-features]
   [--deletion-protection | --no-deletion-protection]
   [--max-allocated-storage <value>]
   [--cli-input-json <value>]
   [--generate-cli-skeleton <value>]

Hope this helps!
-randy

Thanks a lot Randy :) Your advice worked.

aws rds modify-db-instance --db-instance-identifier rds_identifer_name --option-group-name "default:postgres-9-5" --profile abcd

This command should have changed the option group name, but UI shows that both options are attached, and was not allowing to upgrade even after that. After adding any useless security group, using Apply Immediately, it deleted the existing option group :)
Now i can upgrade to 9.6.