You should really update the software. Running old versions of software can be a security risk. We are now at CompleteFTP version 13.1.0.
You can set the minimum TLS which should be used under:
settings (or sites) > HTTP/HTTPS > Advanced HTTP/HTTPS settings > Security Settings (also used in FTPS) > Minimum SSL Version > set the value to TLS 1.2
Please note that setting this value to TLS 1.2 will only allow clients to connect to the server who are also running TLS 1.2. If any of your clients use older legacy machine which only support TLS 1.0. or 1.1 then they will no longer be able to connect to CompleteFTP.