I had up to three different versions on my PC simultaneously without a problem. If you try to install into exactly the same directory, software should tell you that target directory isn't empty ask you, if you are sure to proceed anyway. If you select yes, AFAIK all existing directories and all files in them will be emptied/overwritten. This counts for all later added Logos, silhouettes, outlines, my colours, plane pictures and the database files of course. So, if you want to be sure, you have to back up all this files. The easiest way is to send the directories to a compressed directory like zip or rar. Proceeding that way you can send back all your wanted stuff back after you have Installed the new version.
EDIT: But I'm not 100% sure if it does that way, because it's (unfortunately) ages since I had to upgrade the software to new version. (I hope this coment won't start the next debate about release-time of new version.)
