How to install an extension via Extension Installer in OpenCart 2.x
OpenCart 2.0 got a new way to install extensions by the administrator panel. It's called "Extension Installer" and located in the Extensions part of the admin menu. With this feature, you can install additional extensions from zip archives or single modification XML files.
In order to use the Extension Installer you need to set your FTP access details at default store settings. In order to set it, go to System -> Settings -> Default Store Settings -> FTP Tab. Then set your FTP-host, port, username, password and root folder path, check the Yes radio button and click the Save button at the top right corner of the page.
Pay attention to the field FTP Root, it must include a path from your FTP user root folder to a folder with opencart files and folders like admin, catalog, image and system. Often it's "/public_html/" or "/www/" path but sometimes FTP user could have direct access to the opencart folder and in this case, you must leave the FTP Root field empty.
After setting up FTP access go to Extensions -> Extension Installer then click the Upload button and choose your extension's "*.ocmod.zip" archive or "*.ocmod.xml" file. The uploaded file must have prefix "ocmod" in the name otherwise the Installer will return an error.
If the extension that you are installing contains files with names already existent in the current location, you will receive an alert about this in the "Files that will be overwritten" field. This means the extension is about to overwrite files that you already have on your server. Here, you can either inspect all of the listed files and make sure no OpenCart core files are to be overwritten, or contact the extension's developer directly. Once you are sure it is safe to proceed, click the Continue button. On success, you should get a "Success: You have installed your extension!" message.
If an error occurred during the installation process and the clear button becomes active you need to click it to clear partially uploaded files, solve the problem and reinstall your extension again. Most popular problems with installing an extension by Extension Installer you can find by this link.
Now your extension (module) should be visible in Extensions > Modules. Find it in the Module List and just click the Install button. After this installation your extension may need some configure for this click the Edit button after the extension name in the list. If you can't find the extension in the module list please read this article.
The final step of installation is to apply the changes we have just made. In order to do so, go to Extensions > Modifications and click the Refresh button at the top right corner of the page.