Remove all wpmu sourced software from the website

Hi,

I built a website for a client that utilised a number of your great plugins, but the client decided to go to a competitor for a minor rebrand. I now see that the site has been moved and website design by our company in the footer changed to the competitor. I therefore wish to remove the value added products I originally supplied.
Can you tell me if just deleting the plugins would suffice or is there a better way to remove wpmu from my ex clients website.