Support

Based on your description, I believe that you site is using the wrong tmp directory, hence the problem. Please follow these instructions to change your tmp directory:

1. Go to your site's administrator back-end and click Help, System Info from the top menu.
2. Click on the Directory permissions link
3. Scroll down the page and find the first Cache Directory line. It is the fourth from the bottom of the page.
4. Next to the Cache directory label you can see a path, e.g. /home/myuser/public_html/cache
5. Replace the cache word with tmp in that path, i.e. /home/myuser/public_html/tmp and note down this path. This is your new temp path.
6. Go to Site, Global Configuration menu item from the top menu.
7. Click on the Server link
8. Find the "Path to Temp-folder" and replace its contents with the new temp path from step #5.
9. Save your Global Configuration

At this point, you may have to make the tmp directory of your site writable. In order to do that, here's what you need to do. Create a file named htaccess.txt with the following contents:

order deny, allow
deny from all
allow from none

Upload it to your tmp directory using FTP. After uploading it, change its name to .htaccess (dot-htaccess, there is nothing before the dot) and its permissions to 444. Again using FTP, change the permissions of the tmp directory to 777.

Now, go back to Admin Tools and click on Clean Tmp Directory to remove any leftover files in the tmp directory. Then click on the "Joomla! Update Found" button, let Admin Tools download the update package and try upgrading first using the direct file writes or, of this doesn't work, the FTP method.

If you still get a truncated archive error message, it is possible that your host has file size restrictions which do not allow us to store the entire update archive (yes, that happens sometimes). In this case, we will have to follow plan B. Download the update ZIP package using the link provided by Admin Tools to your local computer. Extract it and remove the "installation" directory (if such a directory exists). Upload all remaining files to your site, overwriting same-named files.

You're welcome!