I think you are trying to update a table and using @update (which is used for variables) instead of update

use this (i just delate @ infront of UPDATE)

string sql = "UPDATE StudNumIPP SET NofStud = '" + noOfStud + "', DBI_IT_Track = '" + dbiItTrack + "', DBI_Biz_Track = '" + dbiBizTrack + "' where acadYear = '" + year + "' AND acadPeriod = '" + period + "' AND Course ='" + course + "' ";