Well, have you tried looking in
Akeeba Backup's download page? Just scroll a little and it's right there.
Now, about the update message. Why do older versions report there's an update available even if it's not supported? This has to do with the Live Update system in use by our software. Older versions of Live Update were not aware of Joomla! version compatibility of available versions of our components, therefore they would report any available newer version as an update you have to install. Changing that required a major change in Live Update and our update server. The change made it in Akeeba Backup 3.5.0 and our other components released after that date. Unfortunately older versions' Live Update code cannot be updated for obvious objective reasons. Releasing updates for older Joomla! versions is also not an option, as it would cause several issues on Joomla! 2.5 sites. Therefore you just have to make sure that you have the latest available release designed for your Joomla! version, as per our Version Compatibility page at https://www.akeebabackup.com/compatibility.html and ignore Live Update's prompts for updating Akeeba Backup.
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!