There are three steps you will need to do:

1)  Install the software

Since you are going to be installing
the software anyway it is a good time to
upgrade to the latest version.  It is free
for the first year and only half price ($34.99US)
after that.  Here are instructions for
downloading and installing the latest version:
http://www.1st-class-software.com/cgi-bin/fom.cgi?file=14
You can purchase the upgrade from:
http://www.1st-class-software.com/orderupg.html

If you choose not upgrade then you will need to
do one of the following:
   a) Install from the diskettes you received when you ordered.
   b) Install from diskettes you made from the 
      TOOLS - MAKE INSTALL DISKS menu option.
   c) Install from the distribution file you downloaded and
      presumably put somewhere for safe keeping.
   d) If you know of another teacher using the same version you
      can have them make you installation disks from the
      TOOLS - MAKE INSTALL DISKS menu option.

We do not distribute old version of our software.  If for some
reason you do not have access to the software from any of the
above sources you will need to go the upgrade route.

2)  Get an unlock key

Here are detailed instructions on how to get an unlock key:
http://www.1st-class-software.com/cgi-bin/fom.cgi?file=17

3)  Load your grades

Use the FILE - OPEN or FILE - RESTORE menu option to load your
grades from your grades backup diskette.  If you are moving grades
from another computer here are detailed instructions:
http://www.1st-class-software.com/cgi-bin/fom.cgi?file=25