When you try to save a change to a table in the SQL Server Databse, sometimes you will get a error message saying "Saving changes is not permitted. The changes you have made require the following tables to be dropped and re-created..." as shown in the below figure.
Due to that you will not be able to change database tables.
You can solve that issue with just a one click. You can find Tools -> Options from SQL Server Management Studio and you will get a Window as shown below. Select Design and under that you can find there is a option saying Prevent saving changes that require table re-creation is selected as shown in the below figures.
Just remove the mark of it and try to save your changes. You should be able to save it unless there are no other issues....