See this
Upgrading or repairing the EROM (FOTA) in phones CID 49 or CID 51 with Phone XS - Top Sony Forums
REPAIRING EROM GUIDES for most sonyericsson phones - Top Sony Forums
In the download section you will find newer version of EROM.

But why do you want to upgrade your EROM? Is your phone broken?... or you want to have a newer EROM