How to write a update query using Sql Compact Server

I want to update 开发者_如何学JAVAcolumn which has datatype of nvarchar. Want to change the column has identity column. Anyone can help?

http://msdn.microsoft.com/en-us/library/ms174123.aspx

It would be smth like

ALTER TABLE <IdentityTable> ALTER COLUMN <Identity Column> <Data Type> (1, 1)

But how're you going to add to nvarchar datatype indentity?