Extension installation is not part of our code, it's part of Joomla!. The error message you posted tells you what is wrong and how to fix it (set the upload_max_filesize and post_max_size on your server's php.ini file). Please go to Extensions, Manage, Warnings and click through the reported warnings for more information straight from the Joomla! documentation.
Furthermore, please refrain from asking support requests in the pre-sales category. This is NOT a pre-sales request, it's a support request for Akeeba Backup and must be filed in the Akeeba Backup category.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!