Unfortunately, an upgrade on one account doesn't apply to other accounts. The expanded storage limit of a Business account won't apply to a personal account.
What happens if my personal account is over quota?
Your Dropbox quota is calculated based on the total contents of your Dropbox, which includes shared folders. A Dropbox account can't sync more than its quota, so a 2 GB account (for example) can't sync more than 2 GB of files, including the space taken up by shared folders. Every member of a shared folder can add and modify the files in the shared folder, so shared folders take up space in each member's account.
Need more space? Consider upgrading to Dropbox Plus or Professional, which have a 1 TB storage limit.
How do I share folders without impacting storage quotas?
If you'd like to share a folder without impacting the recipient's quota, you can share a link to the folder instead. A shared link allows users to view or download a read-only copy of the folder.
If you want to remove a shared folder from your account without affecting other members, you can leave it.
How can I earn more space on my personal account?
If you need more space on your personal account, you can earn bonus space by: