You need to migrate from version 3.1M1 to 3.1M8 only if you want to keep the execution history details (instances and history entries)
If you don't want to keep this information, it's only necessary to export from version 3.1M1 and import in 3.1M8.
If you want to keep the execution history in the new installation of agileWorkflow you have to export the content of the repository (including execution history details) and migrate the exported archive to version 3.1M8.

To migrate from version 3.1 M1 to 3.1 M8:
 * install the "Migrator" application (agileWORKFLOW-migrator-3.1M8_20110831)
 * call the Migrator by executing the following:
        <awf_migrator_directory>\awf_migrator.exe <archive_AWF-3.1M1>.zip
   where <awf_migrator_directory is the installation directory of the application (by default "awf_migrator") 
   and <archive_AWF-3.1M1>.zip is the archive with the export from version 3.1M1
The result will be an archive with the name v3.8.0_<archive_AWF-3.1M1>.zip that updates the execution history details to the last version of agileWorkflow.

Then you can import in your new installation of agileWorkflow (version 3.1M8) this resulting archive.