In terms of availability, just go into the Nokia Store and you'll see the update offered. The core Maps Suite includes Nokia Public Transport, so almost every modern Symbian owner should have the older v2.1 release at least, as did our test Nokia E7 shown here:
The update will pop up automatically in the on-device Store client; (right) 'this might take a while' indeed - over five minutes - go grab a cup of tea!
Finishing the install and starting the new v2.5 for the first time...
The build of v2.5 appears relatively unchanged from the beta, with an official 'build' number rather than a long 'coverage' string. With v2.5, you may remember, your local city will be automatically checked and reported on, even before you start using the application for real.
It's likely that this will be the final version of Nokia Public Transport for Symbian - if you have issues updating from the Store then note that v2.5 is also archived here as NokiaPt_S3_2_5_installer_92_412924.sis.
If coverage isn't yet perfect for your area, note again that the baseline data on the servers is being improved all the time and will continue to be so, due to its use by Nokia's new Windows Phones (where it's called 'HERE Transit' - go figure). So you won't need a new version of the application, you just need a little patience - the data will come to you, effectively!