Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
To transition to your wife's Microsoft 365 Family plan, accept her email invitation using your current Microsoft account. Then cancel your individual subscription and request a refund for the remaining unused time, if you are eligible.
To accept the invitation, open the sharing email from your wife or go to your Microsoft Account Services page and select Accept to join the family group. Your existing Microsoft account, data, and 1 TB of OneDrive storage remain intact because you are continuing to use the same account.
To cancel your individual plan, go to Microsoft Services and Subscriptions, sign in, find your Microsoft 365 Individual subscription, and select Manage, followed by Cancel subscription.
During the cancellation process, check whether Microsoft offers a prorated refund for the unused portion of your individual subscription. Follow the prompts to request the refund if you are eligible. To check if you're eligible : you can do so at this link : https://support.microsoft.com/en-us/account-billing/how-to-get-a-refund-on-a-microsoft-subscription-67dca30b-b323-44d5-acc2-e02f9902c472
More details at https://support.microsoft.com/en-us/accounts-billing/subscriptions/someone-invited-you-to-share-their-microsoft-365-subscription
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hth
Marcin