In that case, you will need to manually upload your extensions. Here are few ways to do it :
- Enable FTP Layer from Global Configuration. Enter your FTP credentials test connection. Then try to install from the Extension manager.
- Download and unzip the extension. Once unzipped, upload the complete folder to your /tmp/ folder. Then goto extension manager and click on INSTALL FROM TEMPORARY FOLDER option. It should automatically pick it up and install it for you.
- Once installed, if you dont see the extension listed on your Joomla backend, you need to do another step. Goto Extension Manager > Discover . Click on DISCOVER on top and it should list the newly installed extension. Simply check it and click on INSTALL to finish the installation.
Here is a nice video explaining this too.