Once you've created a product (a.k.a. plan) and it has subscribers then you will find you cannot edit the price or delivery interval.

The reason for this is to avoid confusion for any existing subscribers / customers. Also there is a technical limitation with Stripe that enforces the same rules for the same reasons.

The Solution

There is a simple clean work around for this. You can "hide" a product from your store by simply throwing the following switching.

Once you have done this, new customers will not be able to sign up to this old plan, now you can create an near identical product and make the changes you want and put it live to "replace" the old version.