You can see that in System, Extensions, Manage. Search for Akeeba Backup in the search box and set the Type drop-down to Package. You will get two entries; one for the old version of Akeeba Backup and one for the new one.
If the oldest version is 8.0 or later the message you received is a problem I have already discovered and addressed. I will release a new version of Akeeba Backup 9 tomorrow.
If the oldest version is older let me know; we'll have to work on it a bit differently.
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!