You can normally just extract the ZIP contents replacing files of the same name.
However in this case many of the files have changed their name (3.4 in the name instead of 3.3). As a result the plist file associated with the app needs modifying to have the new names.
If you have a plist editor on the Mac you can do it yourself. If not, post a message and I will post a .dmg file tomorrow for the 3.4 release that can then act as the basis for using future .ZIP files. Just for reference you might find the
following of use as it is the process I use when putting together the .dmg on a Windows system. The same changes need making if running on OS/X although there the tools will be slightly different.