Convert Office 365 subscription from Personal to Family

I got the Personal subscription for half-price and don't want to lose that discount.

The method to convert a Microsoft Personal subscription to a Family subscription is not straightforward, usually you would need to purchase the Family version, then the remining time on the Personal subscription is converted to a Family subscription at a percentage of the remining time on the Personal subscription, they explain the process on this link.

https://support.microsoft.com/en-us/office/switch-between-microsoft-365-subscriptions-3fcc1efc-2722-427f-8efa-db94b9b0a36b

However in your case, I do not think this process is the best option, I think you should contact Microsoft Support directly to ask them if you can pay the difference between the Personal and Family subscriptions to upgrade the new subscription, try using this method to contact their support.

Go to this link: https://support.microsoft.com/contactus

Select Microsoft 365

Click 'Get Home Support'.

In the box provided, type billing.

Press Enter, then on the next page, scroll down and click 'Sign in to Contact Support'.

Navigate to Microsoft 365 and Office - Manage my Subscription.

Select the 'Chat with support agent in web browser' option