Yes.
With purchase of a Gold Account, storage capacity can be changed in increments of 20 GB*.
It is also possible to revert back to a free account and a 2-GB storage capacity.
However, be sure to take note of the size of data currently uploaded when reducing storage capacity. Changes to storage capacity can only be made once in a single month.
* Gold Account membership with 20 GB of storage space may not be available depending on your region.