Cannot Upgrade to 3.6.3

Hello, I have a crisis. I tried upgrading my Payplans version 3.1 to the latest version because I saw that there was a vulnerability with modifying membership prices. So, I used the installation in the backend of Joomla to install the latest version. It started to install each version (3.1, 3.2, 3.3, 3.4, 3.5) individually until it reached version 3.6.3 then I got the error: "Error ! while processing task : download". I just paid for a new membership and downloaded version 3.6.3 and tried to install it in Joomla backend. Now it says that I have to have Joomla 3.0! I am running Joomla 2.5! The installation prior to my new membership said that I was running 2.5/3.x and that that was fine (see attached screenshot). Please help! PayPlans is not working on my live site. Can you please fix this? Or how can I go back to an older version?