WordPress.org

How can i upgrade from an old version of this plugin?

Deactivate your current plugin, delete the plugin-folder, upload the new one and active it.

How can i get titles under the images?

Go to the "Highslide" option page and uncomment the line '// hs.captionEval = "this.thumb.title";' by removing the slashes. The titles you set in the attachment-dialog of your editor will be shown under the images. Note that really the title will be shown, not the caption. If you like the caption to be shown, change that line to 'hs.captionEval = "this.thumb.alt";'.

Where can i change the appearance of the enlargement?

Change the main appearance on the "Highslide" option page (visit http://vikjavev.no/highslide/doc.php for more information) via JavaScript. You can change the look in detail, if you edit the CSS-file stored in the subdirectory "css" in the plugin folder.

Is it free to use?

Yes, it's free to use. But notice that the highslide player is released under Creative Commons Attribution-NonCommercial 2.5 License and is not free for commercial use! Full text at http://creativecommons.org/licenses/by-nc/2.5/.