Hi Zade,
You will need the admin@system-domain password to upgrade to 5.5.
Reset it by running this script (as suggested in this thread https://communities.vmware.com/thread/428929?start=30&tstart=0)
if SSO password ( admini@system-domain ) needs to be reset, please execute below query on RSA database:
UPDATE
[dbo].[IMS_PRINCIPAL]
SET
[PASSWORD] = '{SSHA256}KGOnPYya2qwhF9w4xK157EZZ/RqIxParohltZWU7h2T/VGjNRA=='
WHERE
LOGINUID = 'admin'
AND
PRINCIPAL_IS_DESCRIPTION = 'Admin';
This will reset the password to "VMware1234!", after which you login and change the password as needed.
Note: Take backup of RSA database before executing this
And then do the upgradation.