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Welcome to the forums, aznbook. 
Since this is the avast forum, there are not many of us who will know how to set up McAfee as you are asking. In fact, many of us, including myself, are former users of McAfee … until we found the best av service, avast!
As oldman stated above, if you are using 2 av programs, you need to decide which one you want to keep and completely uninstall the other one. Using 2 resident av programs actually give your computer less protection than one alone. We hope you will keep avast and delete McAfee.
Whatever av you use to have or if you now have 2, removing an av service with “Add/remove programs” alone will not delete all that needs to be deleted. They will leave behind files … and worse, registry entries … that will interfer with, or be detected by, whatever av program you intend to use now. It is proper to first use “Add/remove programs” to remove whichever you do not want but then you need to use an uninstaller supplied by the deleted av program’s website to remove the left-behind stuff.
By the way, in rereading your post, perhaps you mistakingly typed MvAfee instead of avast. If this is so, please post again so that we can offer the proper help.