Once the code has been installed on your site, you do not need to update the code set if you are changing the styles of the theme or change the sorting and filtering options of the Gallery.
Adjusting the styles of a current theme
To adjust a theme, click on the 'Edit' button for the theme you wish to adjust. Then make the desired adjustments to the styles. Click 'Publish' on the top right of the Theme window.
This action will immediately bring apply the new styles to the associated Galleries. No further action is needed.
If however, you wish to associate a Gallery with a different theme, then you would need to replace the code with the new code made available by clicking the 'Download' button.