Hello @Singh, Shivani !
Hope you are having a Great Day!
Thanks for asking question!
Yes you can Upgrade from Microsoft 365 Single user to Microsoft 365 Family Subscription.
Visit the below mentioned link to know more about the Upgrade.
https://support.microsoft.com/en-us/office/switch-to-microsoft-365-family-or-microsoft-365-personal-3fcc1efc-2722-427f-8efa-db94b9b0a36b
Let me know if you have more questions, I will be glad to assist you.
Regards,
Tasadduq
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