Alter UserDefined Datatype

How can I alter a userdefined datatype.

eg: A user defined datatype of Dt_Quantity numeric(16,0)

Want to change it to numeric(16,3).

Is it possible?

If it requires a system catelog updation please help.

This requirment is came after the implementation of the DataBase.

Please help me fast|||which version of sql server are you using ?|||Using the SQL Server 2005|||

you have to drop it and recreate...

From BOL :

Note: User-defined types cannot be modified after they are created, because changes could invalidate data in the tables or indexes. To modify a type, you must either drop the type and then re-create it, or issue an ALTER ASSEMBLY statement by using the WITH UNCHECKED DATA clause. For more information, see ALTER ASSEMBLY (Transact-SQL).

Madhu