Harvey,
The first thing that I would suggest is to read the "Troubleshooting ..." guide by Dave Stone (here: http://forums.pinnaclesys.com/forums/post/46364.aspx) which outlines all the steps required to upgrade and install Liquid. Since you already have Liquid 7.0, I think that downloading the full installer version of Liquid 7.2 is the way to go. You don't need to have any previous versions installed, just have the 7.0 serial number handy when installing 7.2. Follow the instructions in the "Troubleshooting ..." guide mentioned above and you should be good to go.
If you have problems, by all means come here and ask. We have all gone through growing pains with various versions and can help you to learn to "swim" with Liquid.
I am sure you will enjoy your Liquid experience.