Hi @chyeungc, how are you today?
Yes, that should be possible with the Family plan.
As the manager of a Dropbox Family plan, you can invite up to 5 more members, ages 13 years or older in the United States and 16 or older anywhere else, to join your plan.
The Family plan provides a total of 2TB of storage space to its members.
As to how you can upgrade: do you see the option to do that when you visit this page?
Keep me posted!