Community Builder itself is over 4 MB, and some of its add-ons are well over 2 MB, but some hoster leave PHP's old default upload and POST size limit of 2 MB, making installation not possible by upload.
Check with your web hosting provider for instructions on how to increase your php 'upload_max_filesize' and 'post_max_size' parameters to at least 8M. Or if you are your own hoster or on localhost, check our instructions to change PHP parameters.
Or you can use the "Install from Web" feature of Joomla to install Community Builder, and then the "Install from Web" feature of Community Builder's "Plugin Management" / "Install & Upload" feature instead of using the "Install by Uploading the" feature.