Unzip the downloaded zip package
If you try to install the whole zip package that you downloaded from CodeCanyon, you will get the following error message:
The package could not be installed. No valid plugins were found. Plugin install failed.
That happens because the downloaded zip is not the actual installable plugin, but a bigger folder that contains other assets besides the plugin.
You will need to unzip the package downloaded from CodeCanyon, and inside you will find slider-pro.zip, which is the actual plugin that needs to be installed. Here is a screencast that shows the installation process.
If you are actually having problems installing slider-pro.zip, it probably means that you have an upload limit lower than 4MB, which is the size of the slider. In these situations you will get the following error message:
The uploaded file exceeds the upload_max_filesize directive in php.ini.
What you can do in this situation is either ask the hosting provider to increase the upload limit for you, or unzip slider-pro.zip and FTP the unzipped slider-pro folder in wp-content/plugins/. However, since there are a lot of files, the uploading process can take several minutes. My recommendation is to contact the web host to increase the limit, because you might need a bigger limit with other occasions as well.