>>I knew this would happen; that some day I will mess up my test SQL database and will need to replace it with the backup. Fortunately, I do make routine backups. What I have is the .bak version of the DB. For example, MyTestDatabase.bak; which is on the external drive. And I have the actual database, MyTestDatabase in the SQL Server 2008.
>>What steps should I take to replace the damaged one with the .bak from the external drive?
>>
>>TIA
>
>I created a database, named it 'test'.
>Then I selected this database -> Tasks -> Restore database.
>Selected From Device and located the MyDatabase.bak (on the external drive).
>Checked the box Restore.
>Then error message:
>

>The backup set holds a backup of a database other than the existing 'test' database
>

>
>What am I doing wrong?

You don't need to create a database before restore. There should be an option to give DB new name if you want to restore it under different name