The theme packages come as archive files (usually zip files). To use a particular theme, download the theme package and then unarchive the zip file to your hard drive, preserving the folder structure within the zip file. Then use your FTP application to upload the entire folder to your webserver (into the "themes" sub-folder of your coppermine install.
Example: let's assume that you have downloaded a theme package named cpg1.4.x_theme_foobar
.zip and your coppermine-driven gallery resides in http://your_site.tld/your_coppermine_folder/
. Unpack the archive to your desktop - you should then find a folder on your desktop that is named "foobar
". Upload this folder (using your FTP app) to your webserver into the folder that corresponds to http://your_site.tld/your_coppermine_folder/themes/
Subsequently, you should have a structure on your webserver that looks like this: http://your_site.tld/your_coppermine_folder/themes/foobar/
In the next step, test drive your new theme by adding the parameter "theme=foobar" to the address bar in your browser (in above example, you would go to http://your_site.tld/your_coppermine_folder/?theme=foobar
). Make sure that everything works as expected. If it does, make the new theme (that currently is only visible for you as admin, because you forced the use of this particular theme by adding the URL parameter) the default theme of your coppermine gallery (i.e. make the theme visible for all your site visitors) by going to Coppermine's config, selecting your new theme "foobar" from the dropdown list under "Themes settings" > "Theme" and submitting your change by clicking "Save new configuration" at the bottom of the config screen. Finally, check if your settings stick by resetting your individual theme choice - go to http://your_site.tld/your_coppermine_folder/?theme=xxx