If you are using Shift4Shop's Recurring Orders add-on (a.k.a. Autoship), your users with recurring orders may change the date and frequency of the recurring orders themselves by using the following steps:
Log into their customer profile on your store by using the My Account link.
Once there, look for the "Recurring Orders" section, which will list their recurring orders.
Click on View Details of the order they'd like to cancel.
At the top of the order, they'll see functions available to change the frequency, date and payment method used on the order.
To change the frequency of the order, the user will simply set the frequency to whatever options are made available to them by your module's settings.
Users can also change the date of their next recurrence by changing the "Next Order" date as needed.