I received this error when I try to add a new graphic

I received this error when I try to add a new graphic to the media Center

Upload New Media
Sorry, you have used all of your storage quota of 163 MB.

it's a WordPress mu site with five sub-domains.

Says I have exceeded my limit of 163 MB, showing I have 500 and some megabytes.

They Might have been true at one time. It isn't now?

it was a development site with plenty of action. But I have deleted everything in the root media Center except for maybe 20 or 30 MB.

Questions:
is the media Center and the root common to all the sub-domains?

my original thoughts were that the database lost its index, but I can't find where the pictures are stored in the database.

Any help will be greatly appreciated.
Thanks
Ron