You are currently using OpenVPN Access Server, which is a commercial product from OpenVPN Technologies (the company of the original author). If you're willing to pay, you could contact them for support. Otherwise, you probably want the community version of OpenVPN.
This wiki page has up-to-date information on how to use the available repositories:
Once you've installed the community version, figure out where your OpenVPN AS config files and server keys are (I guess in /etc/openvpn-as, but I never actually ran AS, so I'm not sure), and copy them over to /etc/openvpn. AS is a set of tooling around the community edition for easy administration, so the config files should just work with the community edition.