I recently had to upgrade the Sitecore shared source Poll Module (available on the Sitecore Marketplace) while doing a Sitecore 6.4 to 6.5 upgrade. I couldn't find much of an upgrade path per se, so I went ahead and installed the newer version of the module. Here are a few notes to keep in mind regarding the inevitable overwrites and the necessary cleanup.
All points below stem from the fact that OMS was renamed to DMS.
1) Namespace changes
If you are using any of the Poll Module layouts or skins in your solution, you will probably notice that the namespaces have changed from Sitecore.Polls.OMS to Sitecore.Polls.DMS. All of these will need to be updated for any customized controls to load.
2) Template name changes
The template name has also changed from OMS Poll to DMS Poll, so update any code and configuration where you might be using the template name.
If you have made any changes to the original OMS Poll Item template, you have to be careful to merge them with the new installation package. If you're using TDS (Team Development for Sitecore), you will be able to easily redeploy any custom fields from source control even if the new package installation deleted them.
3) File name changes
All file names have also changed, so after the new module installation, you will need to clean up:
- \sitecore modules\Shell\OMS Poll Module\\*