WordPress.org

As of version 2.3.9, Organize Series requires WordPress 3.3+ to work. Organize Series also requires PHP 5.2+.

ALSO: If you are upgrading make sure you read the upgrade notes.

1. MAKE SURE YOU BACKUP YOUR WORDPRESS DATABASE (that's all in caps for a reason - nothing should go wrong but it's a good precaution nevertheless!!)
2. Download the File (or use the built-in updater provided by WordPress)
3. Extract to a folder in ../wp-content/plugins/. The orgSeries folder can be named whatever you want but the default is "organize-series". The final structure would be something like this: ../wp-content/plugins/organize-series/--and all the orgSeries plugin files/folders--
4. Activate orgSeries on your WordPress plugins page.
5. The Series Icon Feature uses the built in Media Uploader/picker in WordPress.

You can do the above or just use the new plugin install integrated in WordPress.

Upgrading

If you are upgrading from Organize Series 2.1 or above you can follow the same steps as above. Other UPGRADE Notes (for users who are upgrading from Organize Series < 2.2):

1. Your customized seriestoc.php file should still work for Series Table of Contents Pages.
2. Rename your series.php file (series archive pages) to taxonomy-series.php - starting with version 2.2, Organize Series integrates with the built-in taxonomy template pages that WordPress provides. You can also customize a particular series by creating a page titled taxonomy-series-{series-name}.php where 'series-name' is the name of the particular series you want a different archive page/look for.
3. Organize Series Publisher is NO LONGER bundled with Organize Series. Don't worry, you can still get it, it's available on the WordPress plugin repository. Look for organize series publisher.

ALSO

I STRONGLY recommend that you take note of any changes you may have made on the series options page for customizing the layout/look of Organize Series before upgrading. I try to do my best to make sure any changes get imported successfully with updates but sometimes things happen unexpectently and the options may get reset (which can understandably be frustration - believe me, it's happened to me a couple of times over the years!). What I usually do is open a tab with the options and then conduct the upgrade from another tab. That way if something DOES go awry, I can just copy paste from the inputs I left open in the previous tab. Again, I test throughly before releasing an update but I simply cannot account for every possible hosting environment out there so resets can and sometimes do happen.

Other Notes

If you customized the included seriestoc.php file (for Series Table of Contents Page) to fit your site theme better make sure you copy the file over to your theme directory so future upgrades of Organize Series won't overwrite your customizations.

That's it! You might want to read through the Series Options page (as a submenu item under 'options') and the Manage->Series Page. You'll also notice that your "write/edit" posts page now has a handy dandy series box on it for adding your posts to a series (and creating new series on the fly).