Switching iCloud accounts
How do I cancel my iCloud? And join my wife’s?
iPhone 6, iOS 12
Question marked as
If you mean that you want to share your wife's iCloud storage, see the instructions in Share iCloud+ with your family - Apple Support
Your wife will need to share the plan as described in the "Share iCloud+ with everyone in your family" section of that article and you will do as described in the following section:
Switch from your iCloud+ plan to your family plan
When you share iCloud+, any family members using the free 5GB plan are added to your family plan automatically.
If a family member is already paying for their own iCloud+ plan, they can choose to switch to your plan or keep their own and still remain part of the family. When they switch to the shared family plan, they get a refund for the remainder of their personal plan. They can't keep their current plan and use the shared family plan at the same time.