>My Office 365 is coming to end of the first year. So I need to renew the subscription. I see the button Buy in Outlook. But when I click, MS asks if it is ok to make changes to this computer. I don't trust MS as they may start upgrading OS too. Is there a way to Renew Subscription without having MS making changes to my PC?

Maybe you can do it from the Micro$oft store???

http://www.microsoftstore.com/store?Action=DisplayPage&Locale=en_US&SiteID=msusa&id=ThreePgCheckoutShoppingCartPage&wt.mc_id=WEB_Renewal_Default_O365HomeYrCart