How To Alter Column Length Of The Master Table Along With The Slave Table?

In SQL Server 2005,here are two tables, created by the following SQL Statements:

CREATE TABLE student(
ID CHAR(6) PRIMARY KEY,
NAME VARCHAR(10),
AGE INT
);

CREATE TABLE score(
ID CHAR(6) PRIMARY KEY,
SCORE INT,
FOREIGN KEY(ID) REFERENCES student(ID)
);

For the length of Column ID is not enough, So I want to alter its length.The alter statement is:

ALTER TABLE student ALTER COLUMN ID CHAR(20)

For the table student is referenced by table score, the alter statement can not alter the column of the table student, and the SQL Server DBMS give the errors.

But, I can manually alter the length of the column ID in SQL SERVER Management Studio. How to alter column length of the master table(student) along with the slave table(score)?

Thanks!