I got this "side by side" error message also when I tried to install 1.9 (multiple times and downloaded twice). I have never had this kind of trouble before with my other photo editing software or Affinity. I didn't feel comfortable about following the trouble shooting tips out there on the net and uninstalling a perfectly performing version in the hope that then the update will install OK. I have never had to do this with any other program and from the above it seems that for once I did a smart thing! I guess I'll have to give 1.9 a pass and wait for the next version if nothing is done to correct it.