How to change the database collation

ALTER DATABASE [database name] SET SINGLE_USER WITH ROLLBACK IMMEDIATE

ALTER DATABASE  [database name]  COLLATE Newcollation

ALTER DATABASE  [database name]  SET MULTI_USER

For example , suppose if the name of your database is learningdb and you want to change the collation to the collation SQL_Latin1_General_CP1257_CI_AS, then following commands can be used:-

ALTER DATABASE 
learningdb  SET SINGLE_USER WITH ROLLBACKIMMEDIATE

ALTER DATABASE 
learningdb  COLLATE SQL_Latin1_General_CP1257_CI_AS

ALTER DATABASE 
learningdb  SET MULTI_USER