How to identify who made changes in SQL server management?
You have to log the data in some way manually.  My favorite is to include CREATE and UPDATE columns on each table as such:

ALTER TABLE TableName ADD [CREATE_TIMESTAMP] datetime NULL DEFAULT (getdate())
ALTER TABLE TableName ADD [CREATE_USERID] varchar(30) NULL DEFAULT (suser_sname())
ALTER TABLE TableName ADD [UPDATE_TIMESTAMP] datetime NULL DEFAULT (getdate())
ALTER TABLE TableName ADD [UPDATE_USERID] varchar(30) NULL DEFAULT (suser_sname())


Then add a trigger to force the update of the UPDATE columns.
After that you can tell who inserted or updated a row.  Still can't tell a delete though. You would need a log table for that.  Basically create a table TableName_Log that has the same structure as TableName then a DELETE trigger that moves the deleted rows (updated too if you want) into the log table.