How to upgrade your account
If you have a Dropbox Basic account, you can upgrade to Dropbox Plus to get 2 TB of storage space. For 3 TB of storage space, you can upgrade to Dropbox Professional or Essentials.
If you have a Plus or Professional Dropbox account and work with two or more colleagues, you may want to consider upgrading to a Dropbox team account, which starts at 5 TB of storage space.
How to purchase storage space add-ons
Dropbox admins on a Standard, Advanced, Business, or Business Plus account can purchase additional storage space in 1 TB increments only, up to a maximum of 1,000 TB (including space allocated from users/licenses). This additional storage space is pooled for the entire team.
Plus, Professional, or Essentials users can do a one-time purchase of 1 TB storage.