So if you click About in the toolbar it shows your version is 15.3?
If you have the new UX you activate that in Administration > System Options
You should go through the release notes and change and impacts.
Those would tell you more about the changes regarding the new UX. There are also rights involved.
Note that if your URL for the classic UI is
<server name>/niku/nu
for the new UX it is
<server name>/pm