On the web
You can change any account settings at https://www.shopstyle.com/my/settings.
IMPORTANT NOTE: If your account is Cash Back enabled and you want to change your email address: Make sure to change your email address on ShopStyle in your Shopping Preference page (how-to here) AND on Rakuten.com here. Your Rakuten account will not automatically change email addresses.
On the app
From the home page, tap the profile icon in the upper right-hand corner tab > your name > edit your account settings there.