Pl see the feedback regarding database upgrade doc in this thread - Opatch shows incorrect version after applying 184.108.40.206 upgrade
The request is to enhance the doc to add specific steps for Windows, which seem to be missing.
I added a topic to chapter 4 of the Database Upgrade Guide: About OPatch Commands After Upgrading Oracle Database, I added a link to Oracle OPatch User's Guide for Windows and UNIX. The OPatch User's Guide contains an appendix with the commands and syntax for OPatch. You must run OPatch from the new Oracle home after you upgrade.