If you installed the Searchanise extension via Magento Connect, you may not have an opportunity to upgrade right to the latest 3.1.8 version.
The upgrade to the latest version takes several steps.
1. Upgrade the extension through Magento Connect.
1.1. Go to Magento admin panel -> System -> Magento Connent -> Magento Connect Manager.
1.2. Click Check for Upgrades and select Searchanise for update.
1.3. Upgrade to the latest available version (3.1.5).
2. Download the archive file with the latest version of the Searchanise extension.
3. Unpack the archive into the app folder in the root directory of your store.
3.1. Unpack the extension tgz file on your computer.
3.2. Connect to your website source folder with a FTP/SFTP/SSH client and upload all the files and folders from the extension package to the app folder of your Magento installation.
4. Go to the Magento admin panel -> System -> Cache management and clear the cache.