Just delete the old meta tags and paste in the new ones (modifying them for your own business of course). Do this on EVERY page,.. but then go back to all the pages except main page and alter the "Keywords", "abstract" and "Description" tags slightly. You can re-use some words,.. but don't have identical tags on 2 different pages, or Google will drop your ranking sharpish.
Thanks for all the positive comments so far guys,.. it all helps improve the final product.
I'll be doing another 3 or 4 sites this month, so I'll post links when they're nearing completion for more critique!