If you want to run the most recent development version ( not on important live sites please..., unless I asked you to do so ) do the following:
- Go to the Plugins admin page.
- De-activate the plugin.
- Delete the plugin.
- Download the latest development version of the plugin
- On the Plugins -> Add New page click the button and upload wp-photo-album-plus.zip that you just downloaded.
- Activate the plugin
You can look at the header of the Photo Albums -> Settings Admin page, it lists the revision numbers: e.g:
Database revision: 6904. WP Charset: UTF-8. Current PHP version: 7.0.6. WPPA+ API Version: 6-9-04-007.
That's all, you will be sure you have the newest version.
If everything fails and you want to go back to the release version, de-activate, delete and re-install as if it is a new plugin. All settings, albums and photos will survive all your (de-)activations.