A often asked question is: "the Template or the Extension is not possible to install with the Joomla Extension Manager!" - this problem is frequently due to the hosting file upload limit being set too low.
One solution is to upload an extension via the tmp folder. This tutorial looks at how you can utilise this method to install Joomla Extensions or Templates.
An alternative is to increase the hosting account upload limit (although this may not be possible with some hosts).