9.3 beta 5 is a beta, you do not want to install it over a full working x-plane installation. These early betas are usually full of bugs and can totally wipe out a previous installation.
What most long time x-plane users do is either wait for the final version, or create a separate install for the betas... a demo will work as a full install (not time limited) with your x-plane boot disk in the drive.