Should it be just a matter of replacing the DayPilot.dll to upgrade from the Lite version?

No additional changes should be required.

You can give it a try by replacing the Lite version DayPilot.dll with the trial version from http://www.daypilot.org/try/

Thanks for prompt reply.

I replaced 3.0.210.0 with 8.1.3505.1

Needed to change
protected void DayPilotCalendar1_EventClick(object sender, DayPilot.Web.Ui.Events.EventClickEventArgs e)
to
DayPilot.Web.Ui.Events.EventClickEventArgs
but not sure what to do about
protected void DayPilotCalendar1_FreeTimeClick(object sender, DayPilot.Web.Ui.FreeClickEventArgs e)

Am i doing something wrong?

Please take a look at the following guide on upgrading from DayPilot Lite 3.0 to DayPilot Lite 3.1:
http://kb.daypilot.org/13539/how-to-upgrade-from-daypilot-lite-3-0-to-3-1/

The API is compatible since DayPilot Lite 3.1.

FreeTimeClick event has been replaced by TimeRangeSelected event.

Let me know if there is any problem.

Sorry, should have read

Needed to change
protected void DayPilotCalendar1_EventClick(object sender, DayPilot.Web.Ui.EventClickEventArgs e)
to
DayPilot.Web.Ui.Events.EventClickEventArgs

OK, will read.
Many thanks.

Now using dll 5.0.307 and the previous issues have been resolved by following the link you suggested - thanks. However I am confused with the change to 5 which states
TimeRangeSelectedJavaScript uses "start" and "end" variables to store the time range. "{0}" string is no longer replaced with the range start.
and the control documentation which says that " '{0}' will be replaced by the starting time of that slot "

I am probably missing something but it is not immediately obvious to me as my existing code does not work - which I would have expected it to if the dll is simply a replacement.

The API documentation still mentions this options but it is no longer supported (and it will be removed from the documentation in the next version). You can use "start" and "end" variables instead:

TimeRangeSelectedJavaScript="alert('Start date: ' + start.toString());"

Sorry, a few more notes:

1. In the Calendar, it uses start and end variables as I described above.
2. However, the Scheduler still uses {0} and {1} string replacements (for start and resource, respectively). In this point it is incompatible with the Pro version.

Thanks.