[otrs] Upgrade 4.0.13 to 5.0.20 - web UI still "v4"

Greetings, I performed an upgrade on a functional 4.0.13 OTRS system (Linux, MySQL, RHEL6.7) to OTRS v5.0.20. I followed the upgrade process in the OTRS v5 HTML manual. The upgrade appears to have worked but the Agent UI in the browser is still the "OTRS 4 Free" theme. I'm assuming I'd see a v5 default UI. The reason for the upgrade was to get a responsive UI for agents using mobile devices like iPhones. Did I miss a critical step? I'm not sure where this is set. Maybe it's a v4 config file from my running system that needs editing to enable the v5 default UI? Thanks for any suggestions! --Jeff