Change subscription from deluxe to standard?

First, be sure you realise that the Standard version only covers one device. If you need more, you will have to stay with the Deluxe version.

The first thing to do would be to log into your Norton Account and ensure that Automatic Renewal is turned off for your current subscription. Hover your cursor over the user icon at the top right of the Account screen, then click on Manage My Subscriptions. Find your current subscription and look to the right side to find the Automatic Renewal option. Turn that off. That way the current subscription will not get renewed.

Then you can just purchase the Standard version either directly from Norton or from a reputable retailer. If you do make the purchase directly from Norton, the new subscription will start as soon as you pay. So only do this with one or two days remaining on your current subscription because you will lose any remaining time. Purchases from a retailer can be saved until the one or two days remaining regardless of when you pay, so you can take advantage of any sales prices you might find.