"Script table As" does not offer an "Alter to" option in SQL Server 2005 SSMS either.
The Alter can be quite a complicated command, so the scripting wizard does not offer a version of ALTER TABLE. You have to write the ALTER yourself.
Of course, if your needs are simple, you might (1) script out a CREATE TABLE script, (2) then modify it slightly as needed and to have a temporary name, (3) copy the data from the old table to the new one, then (4) drop the old table, and (5)
rename the temporary name to the name you want to use.
But if your table is large, working through how to ALTER it is probably better.