Excellent purchase, you will not be disappointed.

The settings you need to copy are under the Config. tab (native units, ports & pins, motor tuning, etc.).
I think the easiest way is to copy and save your existing Mach3 folder (perhaps rename it to Mach3old), make the new install, then copy over your settings one page at a time (Mach3 saves your settings to <your profile>.xml when it is closed). This will ensure you have a clean and uncorrupted .xml file.
Tweakie.