1. Just use Windows Explorer or the Mac equivalent to copy and paste the fxp file to the new folder. (You can save the fxp files to any folder that you want. Just in case you're not sure about these things: You then have to open the fxp by clicking on the Options menu in the lower right corner of the PianoTeq interface, hovering over FXP, and then clicking on Load fxp from File. From there, you can select the folder where you stored the fxp. Some people store the fxp's in the same folder as the VSTI dll. Other people create an fxp folder that holds all of their fxp's and name the fxp so they can tell which fxp goes with which program. This latter way of working may seem odd, but it keeps all of the fxp's in one place, so you always know where to find them, instead of forcing you to search for the folder where the program file\dll is stored. It also lets you keep different versions of a program installed, and call the same fxp from just one folder.)
2. About uninstalling previous versions of PianoTeq: I don't think that the PianoTeq installation does much in terms of creating code in the registry, so you should be able to uninstall one without doing harm to more recent versions. In any case, if removing the old version causes problems, you can just reinstall the more recent version. I do know that, of course, if you're sure that you have each version of the program in a different folder, including all of the presets, you can simply delete older versions without any harm. But since PianoTeq takes up little space, you may want to keep the older versions--you may find that for some songs, you prefer a preset that has changed slightly in a more recent version. Or you may want to just experiment with what older versions can do, or even mix and match versions, setting up splits in Cantabile or a similar program.