Newbie help, update and add-ons

Hi all, I'm just after a little advice.
I've downloaded a shipping and a store credit add-on as well as the 1.51 update but once I've unzipped them how do I actually update my site with them?

Links to the mods themselves would help, but most mods contain readme files of some sort containing installation instructions.

In addition to what stevesh stated:

Most plugins and constructed in ZenCart form - meaning that using FTP you can drag & drop the folders and the contained files will be transferred

Instructions on using your FTP client can be googled for

BUT do read the documents that each addon has

Additionally....

You sound like you're going to jump on your horse and ride madly off in all directions.

Your first step is to upgrade in a NEW location. NEVER mess with an existing store. And, NEVER - NEVER attempt to install a mod during an upgrade.

Before you do anything else, read http://www.zen-cart.com/entry.php?3-How-do-I-rebuild-my-site-on-the-new-version-instead-of-upgrading