Simply run the installer, it will uninstall the previous version at beginning of the installation process.
Warning: Make sure your LW saved files/shared files are
not within the LW program folder, if they are then move them out. Otherwise the installer will delete the entire LW Program folder & any files within.
So as soon as you install the new version you will find all settings should be the same. However, LW 4.18 does have some changes. See
If you updated LimeWire & cannot find your Downloads. We generally recommended deleting the LW preferences folder after the update, but if you find no problems then just leave it as it is.
LW 4.12 was a good version by the way. However, since the LW 4.17 beta I think it was, LW will no longer connect with versions older than 4.14 (for uploads I think, not sure.) Let us know if you have any problems with LW 4.18.
BTW I would recommend installing using the OFFLINE installer version:
http://www9.limewire.com/download/LimeWireWin-full.exe as it makes for a much safer installation, instead of installing whilst simultaneously downloading most of the program data. The 'offline' installer has all the data within the installer itself, so less chance of hiccups.