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You can find the updated Miva 10 Reference Guide here
Modules are blocks of code that add features to your store. You can use the Modules screen to add modules that you've downloaded from Miva Merchant or a third-party developer. Some modules are available for a fee, others are available as a free download.
When you download a module (either free or purchased) it is generally packaged in a .zip file. The zip file will usually have an instructions document that tells you how to install and configure the module. These instructions can be quite different from module to module, but the general process is as follows:
The module file will have a ".mvc" extension.
The steps to completely remove a module from your store vary quite a bit from module to module. Generally you have to look inside the zip file that the module was package in for the instructions. If the module did not come with instructions on how to remove it, you can either contact the manufacturer who created the module, or call Miva Merchant support.