WordPress Theme installation is simple task, that is the initial part of the installation process. For very basic WordPress themes, with options sufficient just to have website working, theme activation is all you need to do. This is probably due to the fact, that WordPress system as such provides rich functionality.
There are two installation methods: first means that you just click install link on WordPress admin panel for chosen WordPress theme and that is all – WordPress theme is installed, but not activated yet, you still have the old theme active. One more step: click activate button, and your new WordPress theme replaces the old one.
Another option – via FTP upload – is more time consuming and is usually the only way for installation of paid and highly advanced WordPress themes provided by third party companies. After purchase of such theme and download of zipped file (or after download of free theme zipped file from WordPress website) you have to unzip the file and upload the theme folder to (path to your wordpress installation)/wp-content/themes/ . Don’t change name of the unzipped folder. Upload theme folder as is to the mentioned location, preferably in BINARY mode due to the fact that image files could be corrupted if uploaded in FTP TEXT mode. After upload you can activate your new WordPress theme. Just after upload it is not activated, you have to go to Appearance zone of your WordPress admin panel, where you can see all your installed themes, and from there activate the new theme.
Don’t be surprised if after activation, when new WordPress theme replaces the old one, some of your previous features disappear. It can happen, but usually doesn’t mean that you lost your website content. Quick return to previous theme can confirm that everything is OK. In most cases, the new template can intercept WordPress system settings and/or information related to website content and previous theme’s navigation, but not always is able to translate customized settings of previously installed theme.