It’s in the Tray
Down in the tray, near your system clock, there is probably a little red icon asking you to install the Adobe reader patch right now. It looks like this:
It’s the one on the left.
Double-click on that little icon, and you’ll get a screen up that looks like this:
Click install and follow the directions.
From the Reader
If you don’t have the little icon down in the tray, then just launch the Acrobat Reader, either from its red desktop icon or the start menu.
When it’s up, select Help->Check for Updates and follow the instructions.