Installing a Style
From PunBB Resource Wiki
Please note To install styles that uses templates, you'll have to make these changes to your PunBB: Changes
Automatic installation with Style installer
There is an admin plugin called Style installer that can be used to install styles. It requires the webserver to have write permission in the following folders: *img/ *include/template/ *style/ *style/imports/
When everything is ready, pick the install file by using the browse form, and then hit "Install".
If you can't get write permissions, you might consider doing a manual installation.
Sometimes, PHP doesn't have write permissions, and you have to make a manual installation. A manual installation is very simple to do under any *nix platform, where most permission troubles exists. Just download the tar package for the style you want and put it into PunBB root. If using linux and you have shell access, cd into PunBB and write:
tar -xvf style_package.tar
If you don't have shell access nor write permissions with your Web server, you may have to use the Style installer locally then have a look at the log where you can find which files that was extracted. Then simply use FTP or somthing to upload those files to your PunBB directory in the appropriate location.