Hello Marubun Support,
You can't upgrade from 4.1.8 to 4.2 version.
4.1.8 was released after 4.2 was released.
In the 4.2 upgrade documentation as well we do mention 4.1.7 as the highest build that can be upgraded to 4.2
https://techdocs.broadcom.com/us/en/symantec-security-software/identity-security/privileged-access-manager/4-2/upgrading.html
You would have to wait for the next maintenance release 4.2.1 to upgrade from 4.1.8.
Thanks,
Reatesh.