There have been so many changes since 4.8.1!! Have a look at the changelog, you'll be able to see exactly what changes have been made through the versions since then
http://www.limewire.com/english/cont..._history.shtml

If you want to update to 4.12.6 Pro, you'll have to pay again. Or, you could try the basic & get to know it first, then upgrade to Pro if you're happy with it. If you love your 4.8.1, make sure you've saved the installer - just in case you want to revert back to it.

There's a link for downloading a printable version of the user guide here & when you've opened it, you have the option to save a copy on your computer.
http://www.limewire.com/english/content/userguide.shtml

To filter out wma files, add .wma to the keyword filter (tools > options > filters > keyword).