To change the collation of an database following commands can be used:
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_
ALTER DATABASE learningdb SET SINGLE_USER WITH ROLLBACKIMMEDIATE
ALTER DATABASE learningdb COLLATE SQL_Latin1_General_CP1257_CI_
ALTER DATABASE learningdb SET MULTI_USER
