Before you begin make sure you have a recent back-up of your wallet.dat file.
Also make sure your FeatherCoin client is not running.
Download the latest FeatherCoin client from the website (http://www.feathercoin.com).
Extract the files to (for example) your desktop.
Open explorer and browse to your active FeatherCoin wallet location. (i.e. C:\Program Files (x86)\FeatherCoin).
Copy the extracted files from you desktop and paste them in the active FeatherCoin directory (select ‘Yes’ if being asked to overwrite existing files).
Double click the Feathercoin-qt.exe file and you are done!