SQL Server Studio Express Error 1827

I am getting the below error message when trying to increase size of our database in SQL Server 2005. Please help.
TITLE: Microsoft SQL Server Management Studio Express ------------------------------
Alter failed for Database 'CNG_Main'.  (Microsoft.SqlServer.Express.Smo)

------------------------------ ADDITIONAL INFORMATION:
An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.Express.ConnectionInfo)
------------------------------
CREATE DATABASE or ALTER DATABASE failed because the resulting cumulative database size would exceed your licensed limit of 4096 MB per database. (Microsoft SQL Server, Error: 1827)

------------------------------ BUTTONS:
OK ------------------------------