Due to the nature of the plugin you need to change some files from the core code of Interspire Email Marketer.
To simplify process we provide a full copy of the Interspire with our files on it.
If you have not modified the core code, or you are using other plugin that don't modify the core code files you can substitute the files and follow the wizard, it works in the same way as an Interspire update.
If you have modified some core code files, please open a ticket before proceed to the purchase, maybe some extra work has to be done for merging different version.