Changing Populated Field Types

How can I change a field type whilst it is populated?

I have tried :

insert new_table
select *
from old_table

but I get :

Disallowed implicit conversion from datatype 'text' to datatype 'varchar'
Table: 'davy.dbo.new_table', Column: 'de_area'
Use the CONVERT function to run this query.

My table formats are as follows :

TABLE dbo.new_table (
de_pk int NOT NULL ,
de_name char (25) NOT NULL ,
de_area char(255) NULL
)

TABLE dbo.new_table (
de_pk int NOT NULL ,
de_name char (25) NOT NULL ,
de_area text(16) NULL
)