@
gabby98 - this is what I'd do (I've never need to do it though)
- after installing the 64bit version I would copy the Configuration folder to a safe place - last button on Preferences->Miscellaneous will take you into the folder.
- delete everything in there, and then copy the contents of ...Calibre Portable\Calibre Settings into there.
- point the 64 bit version at your library via Library->Switch Create Library,
- should be easy to test - are your plugins there, are settings there etc, if not restore the safe copy and wait for better advice
BR