In addition to @FFrewin's answer, if you do not have FTP access, you can clean the **tmp** folder using [Admin Tools][1]. The option for this is located on the Admin Tools control panel as shown in the below screenshot:

![enter image description here][2]

As mentioned by FFrewin, the Pro version of Admin Tools allows you to perform a scheduled clean up of the **tmp** directory.

In addition to this, you can also install an extension from the **tmp** folder, by following these steps:

 1. In your **tmp** directory, create a new folder, for example **helloworld**
 2. Extract your zip file on your computer and upload the contents to this newly created folder. Depending on your FTP client, you could firstly upload the zip file and *then* extract it.
 3. In the Joomla backend, go to **Extensions** >> **Extension Manager** and on the tabs below, select **Install from Directory**.
 4. You will see a predefined path, such as `/home/xxx/public_html/tmp` which you simply need to add your newly created folder on to, so it would be `/home/xxx/public_html/tmp/helloworld`
 5. Click **Install**

  [1]: http://extensions.joomla.org/extensions/access-a-security/site-security/site-protection/14087
  [2]: https://i.sstatic.net/T8slF.jpg